Psychiatric Comorbidities in ADHD

Author: Ulrich Brennecke
Review 10/2024: Waldemar Zdero, M.A. in Psychology

People with ADHD often have the following psychiatric disorders as well (comorbid), listed in descending order of frequency among people with ADHD (as a percentage of people with ADHD) compared to the frequency among people without ADHD.

Among adults in the top 10% of ADHD symptom severity according to the ADHD-E scale, psychological distress occurred 6.99 times more frequently than among those without ADHD.¹

A study found that 51.8% of people with ADHD had one or more comorbid mental health conditions.²
Another study conducted in Japan in 2019 found that 54.4% of children and adolescents with ADHD had comorbid ASD, and 60.9% of adults had a mood disorder (depression, etc.).³

The percentages in the headings should indicate the prevalence of comorbidity in ADHD. Example: 70 to 80% of children with ADHD suffer from sleep disorders, compared to 35 to 40% of children without ADHD. Unfortunately, the figures are currently mixed up and need to be corrected.

1. Learning Disabilities - Up to 92%¶

1.1. Learning Disabilities in Children - 10 to 92%¶

10–92% prevalence of comorbid conditions in children with ADHD⁴/general learning disability (approx. 20%)⁵⁶

1.2. Learning disabilities in adults - 2% (vs. 1.6%)¶

Total adults: 1.6%; women: 1.4%, men: 2.4%; ADHD-I: 1.5%, ADHD-C: 2.5%, ADHD-HI: 2.5%⁷

2. Autism Spectrum Disorders (ASD) — 3.6% to 85% (vs. 0.40% for girls to 1.85% for boys)¶

People with ADHD are at high risk for comorbid ASD.

• 15- to 21-fold increased risk (based on a population prevalence of ASA of 1%) (meta-analysis)⁸
  • 15% to 21% of children and adolescents with ADHD have an autism spectrum disorder
  • Children with ADHD who also have ASD exhibit more severe ADHD symptoms than children without ASD
• 8.07 times higher risk for children with ADHD (OR = 8.07)⁹
• 24% of children with ADHD met the criteria for ASD¹⁰
• 23% among adults with ADHD (small study, N = 105)¹¹
• a 31% to 37% increased risk of ASA¹²

Children with ADHD who had not been diagnosed with ASD exhibited increased ASD traits¹³, which was associated with negative outcomes in interpersonal, academic, and cognitive domains¹⁴.
The level of autistic traits in children without ASD can be measured using the CBCL-AT scale.¹⁵¹⁶ The CBCL-AT scale is considered positive if the sum of the T-scores for the Withdrawal, Social Problems, and Thinking Problems subscales of the Child Behavior Checklist (CBCL) is 195 or higher. According to this criterion, 18.18% of children with ADHD without autism exhibited autistic traits, compared to 0.87% of children without ADHD (20.9-fold risk, +1,990%).¹⁶

• 60% of children with ADHD exhibited ASD traits.¹⁷¹⁸
• 11.3% diagnostic prevalence of ASD among n = 221,714 people with ADHD (average age 25.1 years) ¹⁹

People with ASD also have an increased risk of ADHD^{620 21 22} It was referred to as:

• 85%²³
• 78% (among N = 83 children with ASD, Asperger’s, and pervasive developmental disorder)²⁴
• 26% (study of N = 103 children, 85% of whom were boys with ADHD without intellectual disabilities—in 27 of these cases, previously undiagnosed ASD was identified)²⁵
• 21.6% of people with ADHD had comorbid ADHD²⁶
• 3.6% across the entire age range (cohort study)²⁷

The DSM-IV still stipulated that ADHD and autism spectrum disorders should not be diagnosed as comorbid disorders. This was changed in the DSM-5.

In a large study, girls with autism who also had ADHD showed significantly more severe symptoms of ADHD, learning disabilities, and ODD than boys with ASD and ADHD.²⁸

In the general population, ASS occurs in 1 out of 54 boys (1.85%) and in 1 out of 252 girls (0.40%).²⁹

There is evidence that ADHD and autism have common genetic roots.³⁰¹² ADHD and ASD share two genes that are known as risk genes.²⁰ There is speculation that ADHD and autism may have additional common genetic roots.³⁰ In ASD, disorders in dopaminergic neurotransmission are suspected, among other things,³¹ while such disorders have been proven in ADHD.

Approximately 28%³² to 50% of people with autism have ADHD as a comorbid condition.
The fact that, according to DSM-IV, ADHD was not to be diagnosed in cases of autism contradicts empirical evidence and has therefore been omitted from the DSM-5.²¹

3. Sleep Disorders - Up to 80%¶

A Swedish registry study found that people with ADHD in all age groups had a 6.4- to 16.2-fold increased risk of being diagnosed with a sleep disorder and a 12- to 129.4-fold increased risk of being prescribed sleep medication.³³

3.1. Sleep Disorders in Children with ADHD - 70 to 80% (vs. 35 to 40% = +100%)¶

70–80%³⁴; 73.3% (28.5% mild plus 44.8% moderate and severe),³⁵⁶ twice as common as in people with ADHD³⁶³⁷
For the treatment of sleep disorders ⇒ Sleep Problems in ADHD.

A meta-analysis found that approximately 33% of all people with narcolepsy also have ADHD.³⁸
Narcolepsy is associated with reduced dopamine levels in the cerebrospinal fluid. This is consistent with the dopamine deficiency seen in ADHD. In dogs with narcolepsy, however, elevated dopamine levels have been found in the amygdala and elevated norepinephrine levels in the oral pontine reticular nucleus. Nevertheless, these dogs respond to stimulants that increase dopamine and norepinephrine.³⁹
Kooij reports that 43% of people with ADHD experience sleep disturbances (difficulty falling asleep or staying asleep).⁴⁰

3.2. Sleep disorders in adults with ADHD - 11.3% (vs. 2.3%)¶

Sleep problems that last longer than a month are called sleep disorders.

• Among adults with ADHD: 11.3%⁴¹ to 29%⁴²
• Among those not affected: 2.3%⁴¹
  = a 5- to 12-fold increased risk

The annual prevalence of sleep disorders in Germany in 2008 ranged from 0.6% (ages 15 to 19) to 6.6% (ages 60 and older) for men and 0.8% (ages 15 to 19) to 7.8% (ages 60 and older) for women.⁴³
Sleep problems are extremely common in people with ADHD:

• 70–80% of children with ADHD have trouble sleeping
• 20–30% of people with ADHD suffer from sleep problems
  Of the 670 adults with ADHD (with a medical diagnosis) who took the ADxS.org online symptom test, 69% reported sleep disturbances, compared with 39% of the 159 people with ADHD who stated they were definitely not affected (as of March 1, 2022).

A meta-analysis found that approximately 33% of all people with narcolepsy also had ADHD.³⁸

3.3. Consequences of Sleep Disorders (Sleep Disorders: Children 47.1%; Adults: 0.6 to 7.8%)¶

A Chinese study of 23,791 schoolchildren found that 68.7% of children with ADHD had poor sleep quality, compared with 47.1% of children without ADHD.⁴⁴

See also: ⇒ ADHD – Comorbidity, specifically regarding sleep problems

When it comes to sleep problems and ADHD, it is difficult to distinguish between cause and effect. ADHD very often causes sleep disturbances, and sleep disturbances often cause ADHD-like symptoms.

When ADHD is diagnosed, comorbid sleep disorders should always be treated as a top priority. In addition, when prescribing medications for sleep problems, their potential negative impact on ADHD symptoms must be taken into account, just as medications for ADHD must be evaluated to ensure they do not exacerbate these sleep problems. More on treating sleep problems in ADHD: ⇒ Treatment of Sleep Problems in ADHD

• Disorders of alertness associated with impairments in sleep-wake regulation⁴⁵⁴⁶
• Consequences of sleep apnea syndrome⁴⁷
  “Obstructive sleep apnea syndrome (OSAS) is the most common sleep-related breathing disorder. Its prevalence is approximately 4% among men and approximately 2% among women.
  ** -obstructive sleep apnea (OSA) is even more common and reaches strikingly high rates, particularly when subgroups are considered. For example, the prevalence is approximately 36% among patients with diabetes mellitus or hypertension, 50% among obese patients, and 83% among patients with treatment-resistant hypertension. Estimates suggest that 80% of male and 90% of female patients with sleep apnea syndrome remain undiagnosed and are therefore not receiving treatment .” **⁴⁸
  Sleep-related breathing pauses in children can lead to cognitive strain, which can cause symptoms similar to those of ADHD.⁴⁹
• chronic sleep deprivation⁴⁵
• Disorders in the sleep-wake cycle can cause the following within a few days:
  • increased irritability⁵⁰
  • increased impulsivity⁵⁰
  • reduced concentration⁵¹
  • reduced attention⁵¹
  • Working memory disorders⁵²

Common symptoms of sleep problems and ADHD:⁵³

• motor hyperactivity, physical restlessness
• Difficulty concentrating
• Attention problems

ADHD symptoms that are atypical for sleep problems:

• Inner restlessness (typical of atypical depression, less common in melancholic depression)
• Impulsivity
• excessive talkativeness (logorrhea, polyphasia)
• Racing thoughts, ruminating
• rapid mood swings
• Dysphoria due to inactivity

Symptoms of sleep problems that are atypical for ADHD:

• Drowsiness
• (Daytime) fatigue

4. Mood Disorders (Depression / Dysphoria / Dysthymia / Mania / Bipolar Disorder) - 30 to 61% (vs. 4.7 to 8.9% = +550%)¶

Dysphoria associated with inactivity is a core symptom of ADHD and not a symptom of depression. Treating dysphoria associated with inactivity with antidepressants would constitute medical malpractice.
⇒ Depression and Dysphoria in ADHD
Of 70 adults with ADHD, 60.7% had experienced a mood disorder at some point in their lives, compared with 25.7% of those without ADHD.⁵⁴

4.1. Depression¶

Depression was found

• According to a large Swedish cohort study, 42.28% (men: 35.60%; women: 40.27%) of adults with ADHD, compared to 4.69% (men: 3.55%; women: 5.87%) of people without ADHD.⁵⁵

• According to another cohort study, 29.9% (across the entire age range) and 55.7% vs. 24.3% in a small study of adults with ADHD.^{54
  27}

• A Norwegian cohort study found major depression in 24.5% (men: 20.3%; women: 28.8%) of adults with ADHD, compared with 5.8% (men: 4%; women: 7.6%) of those without ADHD.⁵⁶

• For children with ADHD:

  • 37%⁵⁷⁵⁸
  • 37.34% (vs. 7.42% among people with ADHD) = 5 times the risk of depression or an anxiety disorder⁵⁹

• for children who are not affected: 8.9%⁵⁸ –14% ⁵⁷
  = four times the risk

• 19.5% diagnostic prevalence of depression/bipolar disorder among n = 221,714 people with ADHD (average age 25.1 years)

• Mood swings (15–75%)⁶⁰

• depressive disorders⁶

• A simple survey conducted by www.adhs-chaoten.net, in which 73 people with ADHD took part, found that a majority suffer from seasonal fall-winter depression.⁶¹ This is very often a consequence of a vitamin D3 deficiency.
  ⇒ Vitamin D3

• Among adults with ADHD: 61.8%⁴¹;

  • Depression (40 to 60%)⁶²; 25%⁴²

• Major depressive disorder (MDD)

  • 32%⁶³
  • at least once in their lifetime for 26.4% of adults with ADHD, compared with 16.2% of people without ADHD⁶⁴
  • Major Depression (6%)⁶³
    = 4 to 5 times the risk

• Depression (adults with ADHD overall: 21.4%; women 32.1%, men 19.8%; ADHD-I 22.3%, ADHD-C 17.6%, ADHD-HI 32.5%)⁶⁵

• The prevalence of major depression in the general population is 7.8%. Among people with ADHD, the prevalence is 18.6%, which is 2.4 times higher.⁶⁶

• Among adults in the top 10% of ADHD symptom severity according to the ADHD-E scale, the incidence of depression is 6.68 times higher than among those without ADHD.¹

• A meta-analysis found depression among people with ADHD and those without ADHD:⁶⁷

  • in the general population at
    • 8.6% to 55% of people with ADHD vs. 1.2% to 12.5% of those without ADHD
  • in clinical cases involving
    • 15.4% to 39.7% of people with ADHD vs. 5.8% to 39.6% of people without ADHD

• Predictors of comorbid depressive symptoms in adults with ADHD include

  • female gender
    • Women with ADHD had a 3.69-fold increased risk of depression. Women with ADHD who used hormonal birth control (the “pill”) had a 5.19-fold increased risk of depression.⁶⁸
  • Cyclothymic affective temperament and few positive coping strategies⁶⁹
  • emotional dysregulation and a dysthymic temperament⁷⁰

4.2. Dysthymia 6.3% (vs. 3.4%)¶

Dysthymia was found in:

• Total number of adults with ADHD: 7.3%; women 9.4%, men 5.4%; ADHD-I 6.3%, ADHD-C 7.6%, ADHD-HI 15%)⁶⁵

• at least once in their lifetime among 6.1% of adults with ADHD, compared with 3.4% of people without ADHD⁶⁴

• The prevalence of dysthymia in the general population is 1.9%. Among people with ADHD, the prevalence is 12.8%, which is 6.7 times higher.⁶⁶

• Dysthymia: 5.7% vs. 1.4%.⁵⁴

4.3. Bipolar Disorders - 4.7% to 33.5% (vs. 3.1% to 14.3%)¶

Bipolar Disorders (“manic/depressive”):

• 33.5% of adults with ADHD, compared with 6.2% of people without ADHD, at least once in their lives⁶⁴

• 19.4% among persons with ADHD; 3.1% prevalence in the general population, meaning a 6.3-fold increase.⁶⁶

• 6.4% of adults with ADHD overall (women 8.3%, men 4.7%; ADHD-I 5.1%, ADHD-C 8.0%, ADHD-HI 10.0%)⁶⁵

• 6%⁴²

• 4.7% (across the entire age range)²⁷

• Among adult psychiatric inpatients with ADHD: 92.2%⁷¹

• Among those not affected: 14.3%⁴¹

• Mania 0.15% (in ADHD across the entire age range)²

• Between 57% and 86% of children and adolescents with bipolar disorder also have ADHD⁷²

One hypothesis (which has not been experimentally validated) views bipolar disorder as an extreme form of ADHD-C. This hypothesis views ADHD and bipolar disorder as disorders of the self-regulation of extracellular dopamine levels:⁷³
According to this theory, ADHD—like bipolar disorder—is characterized by a disorder in the self-regulation of extracellular dopamine levels, such that the DATs operate partially or completely in a mode of inappropriately high dopamine efflux; however, either the range between the lower and upper regulatory limits (where other factors intervene to stabilize dopamine levels) or the DAT homeostasis feedback loop is different. Bipolar disorder has a much narrower range of functional extracellular dopamine levels than ADHD. While ADHD-HI remains emotionally balanced at an elevated extracellular dopamine level and ADHD-I remains emotionally balanced at a reduced extracellular dopamine level, regulation can be achieved solely through D2 autoreceptor regulation.
However, without utilizing the appropriate autoregulation of extracellular dopamine levels, ADHD-C is said to be
When a certain number of DATs are operating in efflux mode, this results in a high extracellular dopamine level. The D2 autoreceptor can regulate this level to varying degrees, resulting in a state with high extracellular dopamine levels (ADHD-HI) or low extracellular dopamine levels (ADHD-I). In ADHD-C, by contrast, extracellular dopamine levels fluctuate between excessively high and excessively low values. Bipolar disorder differs from ADHD-C in that extracellular dopamine levels are even higher than in ADHD-HI and the upper limit of ADHD-C, and even lower than in ADHD-I and the lower limit of ADHD-C. An extremely high extracellular dopamine level in bipolar disorder correlates with a manic phase, while an extremely low level correlates with a depressive phase.
In our view, the following are points of criticism regarding this model:

• In ADHD-C, inattentive and hyperactive-impulsive symptoms occur simultaneously, whereas bipolar disorder involves clear shifts between manic and depressive episodes.
• The hypothesis model does not distinguish between different brain regions.
• From our perspective, it is more conceivable that extracellular dopamine levels in ADHD-C exhibit different states simultaneously in various regions of the brain.
• Not all people with bipolar disorder also have ADHD, but that would have to be the case if bipolar disorder were simply a more severe form of ADHD-C
• Amphetamine-based medications are more effective than methylphenidate in adults with ADHD. Amphetamine causes DAT efflux—a confirmed effect at higher (drug) doses, though it is unclear whether this also occurs at therapeutic doses. If amphetamine also causes DAT efflux at therapeutic doses, then, according to the hypothesis, it should exacerbate ADHD symptoms.

Cyclothymia is another form of affective disorder in which bipolar mood swings occur at shorter intervals and are less severe than in bipolar disorder.
From our perspective, cyclothymia would therefore be a more likely candidate for a “milder” form of bipolar disorder than ADHD.

5. Motor clumsiness up to 60%¶

Source⁶

5.1. Developmental Coordination Disorder (DCD) - 29% to 47%¶

• 47% have developmental coordination disorder (DCD, dyspraxia) among people with ADHD⁷⁴⁷⁵
• over 50%. An online survey of German parents (n = 149) found a significantly higher prevalence of DCD (over 50%), even among parents who had never heard of DCD.⁷⁶
• 34% of boys and 29% of girls with ADHD (n = 755)⁷⁷

Children with DCD were more likely to exhibit ADHD symptoms.⁷⁸
In an online survey of university students (aged 29 and under) in Japan, 7.4% of participants were found to have dyspraxia (≥ 32 points on the AAC-Q, mean 36.2). 17.6% scored ≥ 27 points. Participants without DCD scored an average of 19.5 points. ADHD was found in 3.2% of participants. The AAC-Q scores correlated strongly with the results of the ADHD Developmental Disorder Difficulty Scales Short (r = 0.65), moderately to strongly with the ASD Developmental Disorder Difficulty Scales (short form) (r = 0.55), and moderately with mental health problems as measured by the UPI (r = 0.41). These findings are consistent with other studies that have identified DCD in 7 to 9% of all young adults.⁷⁹

A combination of ADHD and DCD usually represents a more severe phenotype. Despite some shared neural characteristics, ADHD and DCD appear to have distinct etiologies.⁷⁵

Diagnostic criteria according to DSM-5:

1. The ability to learn and perform coordinated motor skills (when given the opportunity to learn these skills) is below the level expected for the child’s age.
2. Motor difficulties significantly impair activities of daily living and affect academic performance, pre-vocational and vocational activities, as well as leisure and play.
3. It begins in the early stages of development.
4. A doctor cannot better explain the motor difficulties by citing an intellectual disability, a visual impairment, or other neurological conditions that affect movement.

The delay usually involves the development of motor skills. Motor milestones are often not delayed.

5.2. Children with gross motor skill difficulties¶

Frequent accidents, bumping into things, bruises. See also “Symptoms of ADHD.”

5.3. Impaired fine motor skills, poor handwriting - 60%¶

Up to 60% of people with ADHD have impaired fine motor skills, such as poor handwriting.⁸⁰

6. Behavioral disorders / social disorders (aggression, antisocial behavior, oppositional defiant disorder) — up to 55%¶

• 30 to 50% of people with ADHD also have ODD or CD.⁸¹
• 30% of adults with ADHD exhibited some form of social behavior disorder⁸²

6.1. Severe Behavioral Disorders (Disruptive Behavior Disorders) - 30 to 50%¶

Prevalence of DBD in Children with ADHD:

• 50%⁸³
• 30 to 50% of people with ADHD also have ODD or CD.⁸¹
• 31% in Iran among children aged 6 to 18.⁸⁴

Recent models for defining externalizing aggressive disorders include

• Disruptive Mood Dysregulation Disorder (DMDD)⁸⁵ and
• Intermittent Explosive Disorder (IED)⁸¹

6.2. Deficient Emotional Self-Regulation (DESR) - 44 to 55%¶

DESR is described as

1. Deficits in self-regulation resulting from physiological arousal triggered by strong emotions
2. Difficulty inhibiting inappropriate behavior in response to positive or negative emotions
3. Difficulty refocusing attention during intense emotions
4. Disruption of behavioral coordination in response to emotional arousal

• DESR differs from the persistent and severe aggressive irritability that is common in (rare) pediatric bipolar disorder.⁸⁶
• The abnormal moods associated with bipolar disorder are not due to a lack of self-control and include additional mood criteria as defined by the DSM-IV. DESR is not associated with an increased risk of bipolar disorder.⁸⁷

Among people with ADHD, DESR was found in

• 55%⁸⁸

• 44%⁸⁷

• in 2% of people without ADHD.⁸⁷

DESR is diagnosed when people with ADHD score between 180 and 210 points on the three scales—anxiety/depression (intense emotions), aggression, and attention (impulsivity)—of the Child Behavior Checklist (CBCL) (an average of between 60 and 70 per scale). Scores above 210 points are no longer classified as DESR but rather as more severe forms of affective disorders (disorders involving dysregulation of mood and behavior). Given the defined diagnostic criteria for DESR—which cannot be met without a high score on the aggression scale—the diagnosis of DESR is likely limited to the ADHD-HI subtype, which phenotypically tends to respond to perceived stress with aggression.
The CBCL scale for aggressive behavior assesses:⁸⁹

1. Argues or disagrees a lot
2. Indicates, cuts to
3. If she is rude or mean to others, she intimidates them
4. Requires a lot of attention
5. Breaks his own stuff
6. Break things that belong to parents, siblings, or others
7. Don’t Obey at Home
8. Don’t disobey at school
9. Gets jealous easily
10. Tends to get into scuffles and arguments
11. Physically attacks others
12. Talk a lot
13. Likes to show off or clown around
14. Is stubborn, grumpy, or irritable; gets annoyed easily by others
15. Shows sudden changes in mood and emotions
16. Talk too much
17. Likes to tease others
18. Has outbursts of anger or a hot temper
19. Threatens, harasses, or intimidates others
20. Is unusually loud

Consequently, significantly more than 44 to 55 percent of all people with ADHD are likely to suffer from emotional dysregulation, although the manifestations of this condition can vary widely.
Research on this topic would also be desirable, taking into account the subtypes and the phenotypic manifestations of intense emotions associated with each (ADHD-HI: externalizing / ADHD-I: internalizing).

6.3. Oppositional Defiant Disorder (ODD) - 26 to 53% (vs. 3.9% = +560% to +1,260%)¶

• 60% ODD prevalence among children with ADHD⁸² We believe this figure has been misinterpreted. In our view, this might apply—if at all—only when considering boys with severe ADHD-HI. Furthermore, * The prevalence figures by gender do not match the overall prevalence cited:
  • 55% among boys
  • 30% among girls
  • 30% of adults with ADHD exhibit a range of social behavior disorders⁸²
• 53% among children and adolescents with ADHD-C⁹¹
  • 63% for ADHD-C and ASD⁹¹, with 80% of people with ADHD-C also exhibiting ASD
  • 28% for ADHD-I and ASD⁹¹
  • 24% for ASA⁹¹
  • 14% for ADHD-I⁹¹
• 39.3% among children with ADHD⁹²
• 35% ODD in children with ADHD⁹³
• 26.1% among Iranian children with ADHD between the ages of 6 and 18⁸⁴
• 0.7% ODD among adults with ADHD (women 0.0%, men 1.7%; ADHD-I 0.0%, ADHD-C 1.5%, ADHD-HI 5.0%)⁶⁵

ODD among those not affected: 3.9%⁴¹
= 8 to 15 times the risk

Children with ADHD had a 147.05-fold increased risk of oppositional defiant disorder (OR = 147.05)⁹

• ODD primarily refers to ADHD-HI (with hyperactivity) and less so to people with ADHD-I (without hyperactivity), since hyperactivity is a manifestation of an externalizing stress response pattern, whereas ADHD-I is a manifestation of internalized stress (freezing, fleeing). ⇒ The subtypes of ADHD: ADHD-HI, ADHD-I, SCT, and others
• We view ODD (Oppositional Defiant Disorder) as a condition that is purely comorbid with ADHD, and therefore not as a symptom of ADHD.
  • On the one hand, Steinhausen describes social behavior disorders as the most common comorbidity of ADHD; on the other hand, *⁹⁴ * Refers to this comorbidity on page 174 as a subtype of ADHD.
  • Aside from the fact that sleep disorders are likely to be significantly more common, we do not consider ODD to be a subtype because its genetic basis cannot be clearly distinguished.
    • A specific polymorphism of the MAO-A gene is cited as a contributing genetic factor for social behavior disorders as well as ADHD (in each case, as one of several interacting specific genes). However, with regard to social behavior disorders, this gene polymorphism appears to play a much greater role, as it is cited much more frequently in that context, whereas ADHD can manifest even without the involvement of this gene (through the interaction of other genes). In the case of ADHD, the MAO-A gene is consistently cited in a subset of people with ADHD who also suffer from behavioral disorders.
    • Another argument in favor of a purely comorbid condition is that medications not specifically indicated for ADHD, such as risperidone, merely reduce aggression but do not alleviate ADHD symptoms, whereas MPH (methylphenidate) can alleviate both ADHD and ODD symptoms equally.⁹⁵
• ODD does not correlate with any of the symptom clusters in the dual/triple-pathway model; thus, at least in this respect, it has a different neurological basis.⁹⁶

Symptoms of Oppositional Defiant Disorder (ODD):

• Frequent and persistent defiance or disobedience toward authority figures
• Argumentative and easily irritated or annoyed
• Deliberate attempts to annoy others or act in a vindictive manner
• Difficulty following rules and exhibiting a pattern of negative, hostile, and defiant behavior

6.4. Social Behavior Disorders / Conduct Disorder (CD) — up to 20.2% (vs. 4.3%)¶

Conduct disorder (CD) is more common in ADHD.⁶

• 20.2% of adults with ADHD, compared with 4.3% of people without ADHD, at least once in their lifetime⁶⁴

• 16% among children with ADHD (18% of boys, 8% of girls).⁸²

• 1.2% for adults with ADHD overall: 1.2%; women 0.7%, men 1.7%; ADHD-I 0.3%, ADHD-C 1.0%, ADHD-HI 10.0%⁶⁵

People with a social behavior disorder are 21 times more likely (compared to persons without the disorder) to also have ADHD.⁹⁷
Social behavior disorders and aggression disorders have their own genetic predisposition associated with a specific polymorphism in the MAO-A gene. ⇒ How ADHD Develops: Genes or Genes + Environment

The prevalence of conduct disorder among children and adolescents was determined by an Iranian study to be:⁹⁸

• 0.58% among children ages 6 to 9
• 0.57% among adolescents aged 10 to 14
• 1.22% among adolescents aged 15 to 18

32% met the criteria for ADHD and ODD at the same time, while 55% met the criteria for ODD.

Symptoms of Conduct Disorder (CD):

• Aggressive or violent behavior
  • Frequent physical altercations
  • Harm to people or animals
  • Bullying or cruelty
• antisocial behavior
  • Frequent disregard for the rights of others
• recurring and persistent patterns of difficulty in accepting social norms
  • Destruction of property
  • Involvement in thefts
  • fraudulent conduct
  • Lies
• Lack of remorse or feelings of guilt for one’s own actions
  • lack of empathy

6.5. Aggressive behavior—over 50%¶

Just over 50%⁹⁹

Aggressive behavior is not a primary symptom of ADHD-HI. Aggression can be a manifestation of stress, but not everyone reacts to stress with aggression, nor does everyone who tends to externalize stress do so.
One piece of evidence supporting the notion of pure comorbidity is that medications not specifically indicated for ADHD, such as risperidone, reduce aggression but not ADHD symptoms, whereas MPH (methylphenidate) can alleviate both ADHD and ODD symptoms equally.⁹⁵

In cases of ADHD, reduced cortisol levels have been reported in conjunction with aggressive behavior.¹⁰⁰
Externalizing stress responses are associated with reduced basal cortisol levels and a diminished cortisol response to acute stress.
Disorders in stress hormone levels, particularly cortisol, are extremely common in ADHD.
⇒ Cortisol in ADHD

See also ⇒ Neurophysiological Correlates of Aggression

7. Anxiety disorders—up to 47% (vs. 19.5%)¶

47.1% among people with ADHD, which is approximately 2.4 times higher.⁶⁶

24% diagnostic prevalence of anxiety and stress-related disorders among n = 221,714 people with ADHD (average age 25.1 years) ¹⁹

The prevalence of anxiety disorders in the general population is 19.5%.¹⁰¹
Generalized anxiety disorder (a type of anxiety disorder) affects up to 5% of children and adolescents and between 3% and 6% of adults.¹⁰²

No genetic overlap was found between ADHD and anxiety disorders. Genes correlated with high intelligence were found to provide protection against ADHD, but not against anxiety disorders.¹⁰³

7.1. Anxiety Disorders in Children - 25 to 38% (vs. 7 to 10% = up to +400%)¶

The prevalence of anxiety disorders among children with ADHD was:

• 37.9% among Iranian children with ADHD between the ages of 6 and 18.⁸⁴
• 37.34% (vs. 7.42% among people with ADHD) = a 5-fold increased risk of depression or an anxiety disorder⁵⁹
• 37% across the entire age range²⁷
• 34%¹⁰⁴
• 25%¹⁰⁵
• 25% ⁹³
• increased (without a percentage)¹⁰⁶
• Children with ADHD had a 24.49-fold increased risk of anxiety disorders (OR = 24.49)⁹

The prevalence of anxiety disorders in the general population is

• about 10%¹⁰⁷
• 7.42%⁵⁹
  = 3 to 5 times the risk
• Anxiety disorders and ADHD appear to reinforce each other. Treating anxiety or ADHD also reduces the symptoms of the other disorder.¹⁰⁸
• Generalized anxiety disorder increased the risk of ADHD by three and a half times, while ADHD quadrupled the risk of generalized anxiety disorder.¹⁰⁹
• 40 to 85% of children with an anxiety disorder also had ADHD¹¹⁰

7.2. Anxiety Disorders in Adults - 44% (vs. 4.9%)¶

According to a large Swedish cohort study, an anxiety disorder was found in

• 4.3% to 47.1% of people with ADHD vs. 0.5% to 9.5% of those without ADHD (meta-analysis)⁶⁷
• 44.65% (men: 37.02%; women: 55.74%) of adults with ADHD, compared with 4.89% (men: 3.64%; women: 6.19%) of people without ADHD.⁵⁵
• 42%, or 20 to 60%, among adults with ADHD⁶²
• 34.3% of adults with ADHD at least once in their lives, compared with 25.7% of those without ADHD.⁵⁴
• 34.5% (19% anxiety disorders and 15.5% phobic disorders)⁴²
• 22.2% (men: 18.2%; women: 26.3%) of adults with ADHD, compared with 5% (men: 3.3%; women: 6.7%) of people with ADHD (Norwegian registry study)¹¹¹

Among adult psychiatric inpatients with ADHD

• 3.9% to 84% among people with ADHD who are hospitalized vs. 5.4% to 40% among people with ADHD who are hospitalized and psychiatric patients without ADHD (meta-analysis)⁶⁷
• 28.6%⁷¹
• 25%¹⁰⁵

Anxiety disorders and ADHD appear to exacerbate each other. Treating anxiety or ADHD also reduces the symptoms of the other Disorder.¹⁰⁸

7.2.1. Generalized Anxiety Disorder - 5.9 to 25% (vs. 2%)¶

• 8% among people with ADHD, compared with a prevalence of 2.6% in the general population—a roughly threefold increase.⁶⁶

• For adults with ADHD:

  • 25%⁶³
  • 5.9% among adults with ADHD (women 7.6%, men 4.4%; ADHD-I 7.1%, ADHD-C 3.5%, ADHD-HI 7.5%⁶⁵
  • 2.9% of adults with ADHD at least once in their lives, compared with 1.4% of those without ADHD.⁵⁴

Prevalence in the general population: 2%⁶³

7.2.2. Social phobia - 5 to 29.3% (vs. 3.5 to 10%)¶

• 29.3% among people with ADHD, compared to a prevalence of 7.8% in the general population—a rate nearly 3.8 times higher.⁶⁶
• 22.8% of adults with ADHD have social anxiety disorder, compared with 6.6% of people with ADHD at least once in their lifetime.⁶⁴
• 18.6% of adults with ADHD at least once in their lives, compared with 10% of those without ADHD.⁵⁴
• 3.5% among adults with ADHD (women 2.5%, men 4.4%; ADHD-I 3.3%, ADHD-C 3.0%, ADHD-HI 7.5%)⁶⁵

7.2.3. Panic Disorder - 1.9 to 4.3% (vs. 2.9%)¶

• 22% of adults with ADHD, compared with 7% of people without ADHD, at least once in their lives⁶⁴
• 8.9% among persons with ADHD; the prevalence in the general population is 3.1%, meaning the rate is nearly three times higher.⁶⁶
• 4.3% of adults with ADHD have experienced it at least once in their lives, compared with 2.9% of those without ADHD.⁵⁴
• 1.9% of adults with ADHD (women 2.9%, men 2.4%; ADHD-I 2.1%, ADHD-C 2.5%, ADHD-HI 7.5%)⁶⁵

7.2.4. Specific Phobias¶

• 35.8% of adults with ADHD at least once in their lives, compared with 14.6% of people without ADHD ⁶⁴

• 22.7% among people with ADHD; the prevalence in the general population is 9.5%, meaning the rate is nearly 2.4 times higher.⁶⁶

• Agoraphobia:

  • 4.0% among persons with ADHD; prevalence in the general population is 0.7%, meaning the rate is approximately 5.7 times higher.⁶⁶

8. Substance Abuse and Addiction—Up to 45%¶

A meta-analysis found substance use disorders:¹¹²

• in the general population at
  • 2.3% to 41.2% of people with ADHD vs. 0% to 16.6% of people without ADHD
• in clinical cases involving
  • 10% to 82.9% of people with ADHD vs. 2% to 72.2% of people without ADHD

9.3% diagnostic prevalence of substance use disorders among n = 221,714 people with ADHD (average age 25.1 years)

Among patients at addiction treatment centers, 21 to 23% are found to be people with ADHD in screening studies¹¹³, which is 4.6 to 9.2 times higher than the prevalence of ADHD in the general adult population (2.5 to 5%). One study found that 45% of people with ADHD¹¹⁴, which is 10 to 20 times higher than the general prevalence

8.1. Substance-Related Addictions / Substance Abuse¶

Of the N = 873 patients at a psychiatric emergency department in a rapidly growing urban district in North Carolina (U.S.) diagnosed with anxiety, depression, schizophrenia, ADHD, bipolar disorder, alcohol abuse, or schizoaffective disorder according to ICD-10, the following were observed:¹¹⁵

• 58% of patients with a history of psychiatric illness tested positive on a urine drug test
• ADHD (n = 135)
  • 34.7% alcohol
  • 20.2% THC
  • 15.3% cocaine
  • 14.9% acetaminophen
  • 12.9% benzodiazepines
  • 12.1% opiates
  • 8.1% amphetamine-type drugs
  • 1.6% barbiturates
• Depression (n = 225)
  • 40.8% acetaminophen
  • 25.6% THC
  • 20.9% alcohol
  • 15.0% opiates
  • 13.7% benzodiazepines
  • 12.6% cocaine
  • 7.4% amphetamine-type drugs
  • 2.1% barbiturates
• Anxiety
  • 30.8% THC
  • 10.3% alcohol
  • 5.1% opiates
  • 5.1% cocaine
  • 4.7% acetaminophen
• bipolar disorders
  • 29.4% THC
  • 27.3% alcohol
  • 16.9% opiates
  • 13.0% cocaine
  • 10.4% benzodiazepines
  • 9.2% acetaminophen
  • 8.2% amphetamine-type drugs
• Schizoaffective disorder (n = 245)
  • 26.1% THC
  • 25.6% alcohol
  • 24.4% acetaminophen
  • 20.8% cocaine
  • 12.1% benzodiazepines
  • 8.7% opiates
  • 5.1% amphetamine-type drugs
  • 2.5% barbiturates
• Schizophrenia (n = 45)
  • 32.6% THC
  • 14.4% alcohol
  • 10.9% cocaine
  • 5.5% acetaminophen
  • 8.7% benzodiazepines
  • 2.2% opiates

Overall, no significant association was found between psychiatric diagnosis and a positive drug screen.¹¹⁵

8.1.1. Substance Abuse - 21.9% to 35% (vs. 2.9% to 3.6%)¶

• 35.12% (men: 39.44%; women: 30.88%) of adults with ADHD, compared to 3.61% (men: 4.40%; women: 2.79%) of people without ADHD (large Swedish cohort study)⁵⁵
• 21.9% (men: 27.5%; women: 16.2%) of adults with ADHD, compared with 2.9% (men: 3.6%; women: 2.1%) of those without ADHD (large Norwegian cohort study)¹¹⁶

Among adult SUD patients at three drug rehabilitation centers in urban Malaysia, the prevalence of ADHD was 47.2%. Compared to people with ADHD, those with ADHD were less likely to have medical comorbidities (84.9% vs. 93.3%), were more likely to have a history of incarceration (80.8% vs. 65.6%), and were more likely to have been incarcerated for the first time before the age of 18 (24.6% vs. 16.8%).¹¹⁷

Substance abuse is a common comorbidity of ADHD.⁶ One possible explanation could be that dopamine deficiency leads to increased expression of CB1 cannabinoid receptors.^{118119 120} THC binds to CB1 receptors.

Of 70 adults with ADHD, 17.1% had a history of substance abuse, compared with 2.9% of those without ADHD.⁵⁴
People with SUD had an ADHD prevalence of 21% (meta-analysis).¹²¹
Among 153 individuals with substance use disorders (98.7% men) at a clinic in India, 33% were diagnosed with ADHD. The prevalence of ADHD varied across specific types of substance use disorders:¹²²

• 47.6% of people with cannabis dependence

• 38.8% of people who use tobacco or smoke

• 33% of people with cocaine addiction and

• 21.5% of people with alcohol dependence.

• The prevalence of ADHD among people with opioid addiction was approximately 50%. ADHD symptoms, particularly impulsivity, increase the risk of opioid addiction. ¹²³

• Among people with ADHD, substance abuse begins, on average, 3 years earlier¹²⁴

• Appropriate medication (particularly methylphenidate) reduces the likelihood of addiction or substance abuse in people with ADHD.

• People with ADHD and comorbid cocaine addiction showed a significant reduction in addictive behavior when treated with stimulants, corresponding to the decline in ADHD symptoms.¹²⁵

A small Norwegian cohort study found no association between ADHD and alcohol or drug abuse,¹²⁶, as did an earlier study,¹²⁷, which found increased alcohol and drug abuse among people with ADHD only when additional externalizing disorders were present.
However, these studies are in clear contradiction to the vast majority of the scientific literature, which reports a significant increase in risk associated with ADHD.

8.1.2. Smoking - 40 to 45% (vs. 22 to 25%)¶

Among people with ADHD, [number] smoked

• 44.8%⁶⁴

• 42%¹²⁸¹²⁹

• 40% ¹³⁰

• 51% of adult psychiatric inpatients with ADHD are nicotine-dependent⁷¹

Among people without ADHD, smoking

• 27% of women and 32% of men in the total population aged 18 and older¹³¹
• 26% (2005)¹³²
• 22.6%⁶⁴

According to the study, the risk of smoking is nearly doubled among people with ADHD (regardless of medication).
Among people with ADHD-HI or ADHD-C, the risk of smoking is doubled.¹³³

ADHD medications, nicotine (smoking), and zinc block the dopamine transporters (DAT)—which are elevated in ADHD—and thereby reduce their overactivity¹³⁴

8.1.3. Alcohol dependence (30 to 39% vs. 5 to 15%) / Alcohol abuse¶

German guidelines now recommend an ADHD evaluation as standard practice for individuals with alcohol addiction.

The risk of alcohol dependence is dramatically higher in people with ADHD.¹³⁵

• in people with ADHD
  • 38.9%⁶⁴
  • 30%⁶³, 25 to 44%¹³³
  • 8.6% of adults with ADHD have experienced this at least once in their lives, compared with 2.9% of those without ADHD.⁵⁴
  • 4.1% among adult psychiatric inpatients with ADHD⁷¹
• among those not affected
  • 5%⁶³ –14.6%⁶⁴

= 6 to 8 times the risk

Conversely, among 153 alcoholics, 43% were found to have had ADHD in childhood and 22% were found to have persistent ADHD.¹³⁶ Another study found that 19% of 100 adult alcohol-dependent individuals in India had been diagnosed with ADHD.¹³⁷

Alcohol/Substance Abuse:

• 1.6% of adults with ADHD exhibited alcohol or substance abuse (women 1.1%, men 2.0%; ADHD-I 0.9%, ADHD-C 2.5%, ADHD-HI 2.5%)⁶⁵

• 18.1% to 22.6%⁶⁴ compared with 19.3% among those not affected⁶⁴

• A small Norwegian cohort study found no association between ADHD and alcohol or drug abuse,¹²⁶, as did an earlier study,¹³⁸, which found increased alcohol and drug abuse among people with ADHD only when additional externalizing disorders were present.

In cases of alcohol dependence, 6 parameters predicted the presence of comorbid ADHD with an AUC of 0.926:.¹³⁵

• reduced self-control
• increased novelty seeking
• Self-transcendence
• Damage Prevention
• Craving
• earlier onset of alcohol use

Self-regulation and novelty seeking together achieved an accuracy of 85%.¹³⁵

8.1.4. Substance-related addictions in general - 7.8%¶

• Among adults with ADHD: 7.8%⁴¹, 20%⁶³ to 50–60%¹³⁹¹⁴⁰
• Among those not affected: 1.9%⁴¹ to 5%⁶³¹⁴⁰
  = 4 to 12 times the risk
• According to another source, the lifetime prevalence of psychoactive substance use is 52% among people with ADHD and 24% among those without ADHD.¹⁴¹
• Of 70 adults with ADHD, 11.4% had experienced substance dependence at some point in their lives, compared with 0% of the 70 adults without ADHD.⁵⁴

8.1.5. Drug Addiction¶

• The prevalence of drug addiction in the general population is 0.6%. Among people with ADHD, the prevalence is 4.4%, which is approximately 7.3 times higher.⁶⁶
• Among adult psychiatric inpatients with ADHD, 7.1% have comorbid substance use disorder.⁷¹
• People with drug addiction are 4 to 5 times more likely to have ADHD¹⁴²
• 15.5%¹⁴³ to 25% of all people with substance use disorders have ADHD¹⁴⁴
• ADHD was found in 11.2% of all adult patients with substance use disorders who used opioids intravenously or benzodiazepines intravenously or intranasally. The prevalence of ADHD was higher among women (15.3%) than among men (10.3%).¹⁴⁵
• For people with ADHD, the risk of substance dependence (addiction) is 2 to 3 times higher than for those without the condition.¹⁴⁶
• For people with ADHD, the risk of nicotine dependence is up to 9 times higher than for those without the condition.¹⁴⁶
• People with ADHD are about as likely to have an addiction as their relatives who do not have ADHD.
  • Cannabis: 67% vs. 72%¹⁴⁰
  • Cocaine: 23% vs. 21%¹⁴⁰
  • Stimulants: 18% vs. 10%¹⁴⁰
  • Hallucinogens: 18% vs. 7%¹⁴⁰
  • Opioids: 16% vs. 3%¹⁴⁰
  • Sedatives: 14% vs. 10%¹⁴⁰
• According to a study, 12% of cocaine users had ADHD as children, and 10% still had it as adults.¹⁴⁷

8.2. Behavioral Addiction / Gambling 5.3% (vs. 2.4%)¶

People with ADHD are more than twice as likely to develop a gambling addiction (5.3% versus 2.4%). Problem gambling is four times as common among people with ADHD (2.4%) as among persons without ADHD (0.6%).¹⁴⁸
Another study found that 1.54% of adults with ADHD had experienced gambling addiction at least once in their lives, compared with 0.39% of people with ADHD.⁶⁴

A study of N = 97 people with gambling addiction found a prevalence rate of ADHD of 26.0% and a prevalence rate of ASD of 29.8%.¹⁴⁹
A study found that genetic variants associated with substance use may causally increase the risk of ADHD.¹⁵⁰

8.3. Substance abuse (illegal drugs: 10%, nicotine: 16.6 to 25.5%)¶

Among people with ADHD, the prevalence of substance abuse is 33.5%.¹⁵¹ The risk of substance abuse among people with ADHD in the United States is 1.7 to 7.9 times higher.¹⁵²

If ADHD is accompanied by aggressive and oppositional-defiant behavior as well as low self-esteem, the likelihood of substance abuse is significantly increased, whereas no higher rate of substance abuse was observed among people with ADHD who did not exhibit these additional symptoms.¹⁵⁷¹⁵⁸

In our assessment, substance abuse is much more likely to be a consequence of ADHD than a cause of a full spectrum of ADHD symptoms. In rarer cases, it occurs as a comorbid condition. Treatment with stimulants very often eliminates the tendency toward addiction in ADHD. Modern formulations of stimulant medications are barely suitable for abuse as a drug (e.g., Vyvanse: a lysine-bound prodrug of amphetamine that is converted very slowly into the active ingredient only in the intestine).

In the Continuous Performance Test, people with ADHD showed more responses to the correct timing cues than people with substance use disorders.¹⁵⁹

8.4. Addiction / Dependence (Alcohol: 5%, Gambling: 0.31%)¶

Prevalence: Occurs in 24.9% of adults with ADHD.¹⁶⁰

Alcohol:¹⁵⁵

• Dependency
  • Men 4.8%
  • Women 2%
• Abuse
  • Men 4.6%
  • Women 1.5%

In Berlin, 5.0% of respondents aged 15 to 64 met the criteria for alcohol dependence according to the DSM-IV (men: 6.4%, women: 3.5%).¹⁶¹

In Germany, the prevalence of gambling addiction is 0.31%, and the prevalence of problematic gambling behavior is 0.56%.¹⁶²
A study of N = 97 people with gambling addiction found a prevalence rate of 26.0% for ADHD and 29.8% for ASD.¹⁴⁹

When ADHD and addiction co-occur, there is a higher likelihood that ADHD is the underlying cause of the addiction, rather than the addiction being the cause of ADHD. This has been observed, at least, in the case of smoking, cannabis, and likely alcohol as well.¹⁶³

A study found that elevated genetic risk scores for ADHD (polygenic risk scores, PRS) were associated with a 20% increased likelihood of substance use disorder. There were no differences in the severity of substance use (use, abuse, dependence) or the type of substances used (alcohol, cannabis, other illegal drugs). Conversely, the ADHD PRS accounted for only 0.2% of the probability of addiction compared to other risk factors.¹⁶⁴

A study found a prevalence of ADHD of 16.7% among people with severe addiction, compared with 2.5% in the control group.¹⁶⁵
Even more significant was the fact that 53% of severely addicted individuals exhibited socially disruptive behavior during childhood or adolescence (up to age 15), as measured by the SKID-II (compared to 2.5% of control subjects).¹⁶⁶ An early social disorder (OR = 35.1), compared to childhood hyperkinetic behavior (OR = 5.7), represents by far the greater risk factor for severe addiction.¹⁶⁷
To us, this suggests that addiction plays a greater role in ADHD-HI than in ADHD-I.
In terms of substance preferences, there are indications of more frequent use of cannabis products among people with (previous) hyperkinetic behavior. There does not appear to be a significant difference regarding opiates, cocaine, amphetamines, sedatives, and hallucinogens.¹⁶⁸
Although the co-occurrence of hyperkinetic and socially disruptive behavior is associated with early-onset use of illicit drugs, statistically, only earlier and more frequent nicotine use has been demonstrated.¹⁶⁸
Adults with ADHD and substance use disorders began using substances at a younger age and used the following substances:¹⁶⁹

• Most common: alcohol, cannabis, methamphetamine, tramadol
• less common: methylphenidate, methadone, ecstasy, morphine, hypnotics

Chronic abuse of dopaminergic drugs (cocaine, amphetamines) leads to a long-lasting downregulation of dopamine levels. Withdrawal symptoms then correspond to those of ADHD. ¹⁷⁰ Against this backdrop, the question arises as to whether ADHD medications (stimulants)—which are known not to produce any intoxicating effects—might be helpful during withdrawal from dopaminergic drugs.
People with ADHD and comorbid cocaine addiction showed a significant reduction in addictive behavior when treated with stimulants.¹²⁵

Common symptoms of addiction/substance abuse and ADHD:⁵³

• Impulsivity
• (internal) restlessness, motor hyperactivity
• Difficulty concentrating
• excessive talkativeness (logorrhea, polyphasia)

ADHD symptoms that are atypical for addiction or substance abuse:

• Racing thoughts, ruminating
• Attention problems
• Dysphoria due to inactivity
• Mood swings

Symptoms of addiction/substance abuse that are atypical for ADHD:

• Substance Abuse:
  • excessive consumption of a substance, even when there are serious Consequences
• Addiction:
  • excessive use leading to drug dependence
  • very hard to stop

9. Restless Legs Syndrome (RLS, akathisia) - 11 to 44% (vs. 2.6 to 15.3%)¶

A meta-analysis found RLS in 11 to 42.9% of children with ADHD and in 20–33.0% of adults with ADHD. In the general population, RLS was found in 2.6 to 15.3% of people.¹⁷¹ Another meta-analysis (k = 9) found a prevalence of 11 to 54% among children with ADHD.¹⁷²
A study of people with ADHD (ages 6 to 16) found that 33.3% had RLS.¹⁷³ Other sources cite a rate of 44%.¹⁷⁴ A smaller study of adults with ADHD found that 20% had RLS, and that comorbid RLS exacerbated ADHD symptoms.¹⁷⁵
Kooij estimates that 30% to 40% of people with ADHD also have RLS.⁴⁰
One study found that 10% of people with ADHD had a disorder of periodic limb movements (PLMS) (more than 5 per hour).¹⁷⁶ Another study found a PLMS index of more than 5 per hour in 66% of all children with ADHD, which is a marker for RLS, while none of the children without ADHD had an elevated PLMS index.¹⁷⁷ A meta-analysis found no evidence of more frequent PLMS in ADHD.¹⁷⁸
Among adult psychiatric inpatients with ADHD, 25.5% had RLS.⁷¹
A large cohort study found a strong correlation between restless legs syndrome and ADHD.¹⁷⁹

Up to 26% of people with RLS also have ADHD.¹⁷⁴

Regardless of ADHD, RLS occurs in about 2% of all children and adolescents, with 0.5 to 1% experiencing moderate to severe symptoms. Among adults, it affects 5 to 10%. For 25% of people with ADHD, the disorder begins between the ages of 10 and 20.¹⁸⁰ Other sources cite a prevalence of RLS of up to 8%.¹⁸¹
In 70% of cases, people with ADHD are also affected.

No genetic link between RLS and ADHD has been established to date. It is conceivable that the BTBD9 gene, which is associated with iron stores, plays a role.
69.4% of children and adolescents with RLS have sleep disturbances (vs. 39.6% of those without the condition), and 80.6% have a history of “growing pains” (vs. 63.2% of those without the condition).¹⁸¹

10. Cognitive Disengagement Syndrome, CDS (SCT) - 41.3%¶

CDS (formerly known as Sluggish Cognitive Tempo, SCT) was found in 41.3% of people with ADHD in an Iranian study.¹⁹⁷

11. Specific Learning Disabilities - up to 40%¶

Source⁶

A study found specific learning disabilities in 6.6% of children between the ages of 7 and 11. Reading difficulties were found in 4%, math difficulties in 3.6%, and difficulties with written expression in 1.8%. Approximately 63% of children with specific learning disabilities had one or more comorbid diagnoses, with ADHD being the most common comorbidity, found in 54.9% of cases. Boys were affected more frequently.¹⁹⁸

11.1. Reading difficulties, dyslexia—8 to 40% (vs. 5.6%)¶

A distinction must be made:

• Reading and Spelling Difficulties (LRS): an acquired, temporary difficulty, usually caused by external circumstances
• Dyslexia: a genetically caused disorder affecting reading and writing that cannot be overcome through normal practice
• Dyslexia (reading difficulty): Impaired ability to read and understand words or texts, despite normal vision and hearing. Learning disability.
• Alexia: complete loss of the ability to read

8–39%¹⁹⁹²⁰⁰ , 25–40%⁸⁶, 40%¹⁰⁴

Dyslexia and ADHD share significant genetic overlap.²⁰¹²⁰² There is no evidence of a causal relationship between the two.²⁰²
A study found only weak evidence of overlapping neurophysiological changes in ADHD and dyslexia.²⁰³

According to teacher assessments, 6-year-olds with reading difficulties are about four times as likely to have ADHD (21.0% versus 5.6%), and according to parent assessments, they are about twice as likely to have ADHD (30.5% versus 17.8%) as children without reading difficulties.²⁰⁴
There is evidence that reading difficulties associated with ADHD are associated with different patterns of brain connectivity than reading difficulties not associated with ADHD.²⁰⁵

65 to 70% of all children with reading and spelling difficulties are said to have functional binocular vision disorders:²⁰⁶

• Oculomotor dysfunction (OMD) (9%)
  • Impaired fixation
  • Impaired follow-through movements
  • Impaired horizontal eye saccades
• Dysfunctional binocular vision (DBV) (16%)
  • Heterophoria
  • Suppression
  • Convergence insufficiency
  • Accommodative dysfunction
  • Insufficient fusion
  • Insufficient stereopsis
• DBS and OMD (51%)
• Neither DMS nor OMD (24%)

A study of 1,260 children in Pakistan found that 21.2% had dyslexia and 7.6% had ADHD:²⁰⁷

• 192 cases of dyslexia (15.2%)
• 76 cases of dyslexia and ADHD (6.0%)
• in 20 cases of ADHD (1.6%)

11.2. Spelling difficulties (agraphia, dysgraphia) - 12 to 40%¶

12–27%⁵, 25–40%⁸⁶, 40%¹⁰⁴
This is also true for adults with ADHD.²⁰⁸

11.3. Math Difficulties (Dyscalculia) 12–27%¶

12–27%⁵
A meta-analysis found that reading difficulties correlate more strongly with math difficulties than with ADHD.²⁰⁹
This is also true for adults with ADHD.²⁰⁸
ADHD and dyscalculia appear to share common genetic causes. No evidence of a causal relationship between the two was found.²⁰²

Mathematical performance is thought to correlate less with ADHD itself than with executive function problems associated with ADHD.²¹⁰ In individuals with ADHD, math problems correlated with working memory problems, but not with anxiety.²¹¹

11.4. Face Recognition Disorder (Prosopagnosia)¶

It is unclear whether face recognition difficulties are more common in people with ADHD. Some sources suggest they are²¹², while others suggest they are not²¹³.

11.5. Difficulty Remembering Names¶

Difficulty remembering names is said to be more common in people with ADHD.²¹²

11.6. Speech Disorders¶

Speech disorders are said to be more common in ADHD.⁶

11.7. Difficulty Distinguishing Right from Left¶

Difficulty distinguishing right from left correlates with ADHD.²¹⁴
The overall prevalence of right-left confusion among medical students was 14.7%.

12. Developmental disorder—up to 37.4%¶

Developmental disability (Total adults with ADHD: 24.7%; women 25.6%, men 23.8%; ADHD-I 22.6%, ADHD-C 25.6%, ADHD-HI 37.5%)⁶⁵

12.1. Specific developmental disorders - 37.4% (vs. 13.4%)¶

• among children with ADHD: 37.4%⁴¹
• Among those not affected: 13.4%⁴¹
  = three times the risk

12.2. Specific developmental disorders affecting academic skills - 23% (vs. 2.8%)¶

• among children with ADHD: 23.0%⁴¹
• Among those not affected: 2.8%⁴¹
  = an 8-fold increase in risk

13. Bipolar Disorders - 4.5 to 35.5% (vs. 0.2 to 3.6%)¶

Bipolar disorder was diagnosed in

• 14.29% (men: 9.95%; women: 18.95%) of adults with ADHD, compared to 0.72% (men: 0.53%; women: 0.91%) of people without ADHD (large Swedish cohort study)⁵⁵
• 10.9% (men: 8.9%; women: 12.9%) of adults with ADHD, compared with 1.3% (men: 1.1%; women: 1.6%) of people without ADHD.⁵⁶
• 6%⁴²; (Total adults with ADHD: 6.4%; women 8.3%, men 4.7%; ADHD-I 5.1%, ADHD-C 8.0%, ADHD-HI 10.0%)⁶⁵
• 5.1% of adult psychiatric inpatients with ADHD⁷¹
• 4.7% (across the entire age range)²⁷

Among the 2.4 million people studied, 9,250 cases of bipolar disorders were observed. If ADHD was present beforehand, the lifetime risk of bipolar disorder increased 12-fold; if both ADHD and an anxiety disorder were present beforehand, the risk increased 30-fold compared to individuals without ADHD or an anxiety disorder.²¹⁵

People with bipolar disorder have an ADHD prevalence of:

• 60% (meta-analysis of twenty studies involving N = 2,722 PBD patients (mean age = 12.2 years))²¹⁶
• 27% among people with ADHD who are in a manic phase²¹⁷
• 25% (n = 703 adults with bipolar disorder), with men and people with bipolar I disorder more frequently having comorbid ADHD.²¹⁸
• Increased by a factor of 3.06²¹⁹

A meta-analysis found bipolar disorder in people with ADHD and in those without ADHD:⁶⁷

• in the general population at
  • 4.48% to 35.5% of people with ADHD vs. 0.2% to 3.6% of people without ADHD
• in clinical cases involving
  • 7.4% to 80% of people with ADHD vs. 2% to 19.5% of people without ADHD

A study found evidence of overlap in the genetic causes of bipolar disorder and ADHD, particularly in early-onset bipolar disorder (under age 21);²²⁰ another study also found genetic overlap between bipolar disorder and ADHD.²²¹

14. Personality Disorders (in Adults) - 11.5% to 33.2% (vs. 0.9% to 1.4%)¶

Personality disorders are generally not yet diagnosed in children.

The following prevalence rates were found among adults:

• 11.5% (men: 9.1%; women: 13.6%) of adults with ADHD, compared with 1.4% (men: 1.1%; women: 1.7%) of people without ADHD.⁵⁶
• 33.2% among adults with ADHD⁴¹ to 80.3% among adult outpatients at clinics with ADHD²²²
• Among those not affected: 0.6%⁴¹
  = 50 times the risk

A meta-analysis found personality disorders:¹¹²

• in the general population at
  • 0.31% to 33.8% of people with ADHD vs. 0% to 3.9% of people without ADHD
• in clinical cases involving
  • 21.9% to 65.95% of people with ADHD vs. 6.6% to 34.4% of those without ADHD

14.1. Antisocial PS - 18% (vs. 2 to 3.5%)¶

A study found antisocial personality disorder in 18% of people with ADHD-HI who exhibited hyperactivity, compared to 2% of people without the condition.²²³.
Other sources cite 37.1%²²⁴⁸⁹ .
A study found that 18.9% of adults with ADHD had exhibited antisocial behavior at least once in their lives, compared with 3.5% of people with ADHD.⁶⁴

Of 30 people with ADHD-HI in prison, 96% also had antisocial personality disorder.
In contrast, no antisocial personality disorder was diagnosed in 20 people with ADHD-HI who were not in prison and 18 people without ADHD.Interestingly, amphetamines are the most commonly used drugs among prison inmates with ADHD-HI.¹³¹ As is well known, amphetamines are a highly effective medication for ADHD.

Among offenders convicted of domestic violence who had ADHD, ADHD treatment reduced domestic violence to a far greater extent than interventions specifically aimed at addressing domestic violence.²²⁵

14.2. Borderline Personality Disorder / Emotionally Unstable Personality Disorder - 18 to 33% (vs. 1 to 5%)¶

It is estimated that 18.3% of adults with ADHD also have BPD.²²⁶
A population-based study found that 33.7% of people with ADHD also had borderline personality disorder (BPD) (compared with 5.2% in the general population).⁶⁴
A Swedish cohort study found that people with ADHD had a 19.4-fold increased risk of comorbid borderline personality disorder.²²⁷ 3.9% of the more than 2 million participants had a diagnosis of ADHD (3.0% of women, 4.8% of men), and 0.5% had BPD (0.8% of women, 0.1% of men). People who had relatives diagnosed with ADHD also had an increased risk of BPD:

• Identical twins: N = 9,130, OR = 11.2 (Among 9,130 twins, the risk of BPD was 11.2 times higher if the other twin had ADHD)
• Fraternal twins: N = 17,350, OR = 1.0
• Full siblings: N = 2,211,396, OR = 2.4
• Maternal half-siblings: N = 332,486, OR = 1.4
• Half-siblings on the father’s side: N = 331,080; OR = 1.5
• Cousins whose parents are full siblings: n = 6,456,848; OR = 1.5
• First cousins on the mother’s side: N = 472,212; OR = 1.3
• Cousins’ paternal parents’ half-siblings: N = 466,836; OR = 1.2

The risk of a BPD diagnosis when people with ADHD or full siblings had ADHD was:²²⁷

• 19.1 times higher in women (OR = 19.1)
• 21.8 times higher in men (OR = 21.8)

People with ADHD who had the condition as children were 14% more likely to be diagnosed with BPD later.²²⁸

BPS among people with ADHD: 35.7%²²⁴⁸⁹

Among adult psychiatric inpatients with ADHD: 30.6%⁷¹

People with BPS have an ADHD prevalence of 30 to 60 percent.^229230231232

For the differential diagnosis of ADHD and borderline personality disorder, see ⇒ Emotionally Unstable Personality Disorder / Borderline In the article ⇒ Differential Diagnosis of ADHD in the chapter at ⇒ Diagnosis.

14.3. Anxious PS - 10.6% (vs. 2.1%)¶

A study found that 10.6% of adults with ADHD had experienced avoidant PS at least once in their lives, compared with 2.1% of people without ADHD.⁶⁴
Among adult psychiatric inpatients with ADHD: 31.6%⁷¹

14.4. Insecure PS¶

27.1%²²⁴⁸⁹

14.5. Compulsive PS - 19.3 (vs. 7.8%)¶

A study found that 19.3% of adults with ADHD had experienced compulsive PS at least once in their lives, compared with 7.8% of people without ADHD.⁶⁴
40.7%²²⁴⁸⁹

Among adult psychiatric inpatients with ADHD: 10.2%⁷¹

14.6. Combined PS¶

Among adult psychiatric inpatients with ADHD: 25.5%⁷¹

14.7. Paranoid PS - 14.8% (vs. 4.1%)¶

20.0%²²⁴⁸⁹
A study found that 14.8% of adults with ADHD had experienced paranoid delusions at least once in their lives, compared with 4.1% of people without ADHD.⁶⁴

14.8. Dependent PS - 3.1% (vs. 0.4%)¶

15.7%²²⁴⁸⁹
A study found that 3.1% of adults with ADHD had experienced substance dependence at least once in their lives, compared with 0.4% of people without ADHD.⁶⁴

Among adult psychiatric inpatients with ADHD: 18.4%⁷¹

14.9. Narcissistic PS¶

15.7%²²⁴⁸⁹
A study found that 25.2% of adults with ADHD had experienced narcissistic personality traits at least once in their lives, compared with 5.7% of people without ADHD.⁶⁴

14.10. Histrionic PS - 10.7% (vs. 1.6%)¶

14.3%²²⁴⁸⁹
One study found that 10.7% of adults with ADHD had experienced histrionic personality disorder at least once in their lives, compared with 1.6% of people without ADHD.⁶⁴

14.11. Schizotype PS - 22.4% (vs. 3.5%)¶

8.6%⁸⁹
A study found that 22.4% of adults with ADHD had schizotypal personality disorder at least once in their lives, compared with 3.5% of people without ADHD.⁶⁴

Former terms: borderline schizophrenia, latent schizophrenic reaction, pseudoneurotic schizophrenia

14.12. Schizoid PS - 9.2% (vs. 2.9%)¶

6.4%⁸⁹
One study found that 9.2% of adults with ADHD had experienced schizoid personality traits at least once in their lives, compared with 2.9% of people without ADHD.⁶⁴

15. Premenstrual Dysphoric Disorder (PMDD) - 31.4% (vs. 9.8%)¶

Premenstrual Dysphoric Disorder (PMDD) is a severe form of premenstrual syndrome (PMS). It occurs in the days leading up to menstruation and subsides once menstruation begins. Symptoms include

• Mood swings
• Irritability
• Feelings of anxiety
• Difficulty concentrating
• depressive moods.

PMDD was reported by 31.4% of women with a self-reported ADHD diagnosis and by 41.1% of women who screened positive for ADHD using the ASRS, compared with 9.8% of women without ADHD.²³³

16. Tic disorders 30% (vs. 5%)¶

Source⁶²¹

Approximately 30% of all patients with ADHD have tics or Tourette syndrome, while about half of all patients with a tic disorder or Tourette syndrome also have ADHD.²³⁴
The prevalence of tic disorders in the general population is approximately 5%.²³⁵

17. Post-Traumatic Stress Disorder (PTSD) - 11.9% to 28% (vs. 3.3% to 6%)¶

• The prevalence of PTSD in the general population is
  • 3.3%⁶⁶
  • 6% lifetime prevalence⁶⁴

The following prevalence rates of comorbid PTSD were found among people with ADHD:

Meta-analyses:

• 28 to 36% among adults with ADHD (meta-analysis, k = 21)²³⁶

Studies:

• 0.7% of adults with ADHD overall⁶⁵
  • 0.7% women
  • 0.7% men
  • 0.9% ADHD-I
  • 0.0% ADHD-C
  • 2.5% ADHD-HI
• 11.9%, representing an increase of about 3.6 times.⁶⁶
• 22% of adults with ADHD⁶⁴
• 26.5% among adult psychiatric inpatients with ADHD⁷¹
• The comorbidity of ADHD and PTSD was 32% more common in women than in men, but this was true only for adults (meta-analysis, k = 13, N = 13,585)²³⁷

PTSD is associated with a significantly increased risk of ADHD (up to +153%)

• 2.53-fold increased risk of ADHD (+153%) among war veterans with a history of PTSD²³⁸
• 2.19-fold increased risk of ADHD (+119%) among war veterans with existing PTSD²³⁸

18. Impulse Control Disorder (ICD) - 19.6% (vs. 6.1%)¶

• The prevalence of impulse control disorders (ICD) in the general population is 6.1%. Among people with ADHD, the prevalence is 19.6%, which is approximately 3.2 times higher.⁶⁶
• Total adults: 2.6%; women: 2.9%, men: 3.7%; ADHD-I: 1.2%, ADHD-C: 5.0%, ADHD-HI: 12.5%⁶⁵

Impulse control disorders are characterized by a recurring, irresistible urge to engage in certain behaviors that harm the person with ADHD or others and are often associated with feelings of guilt or shame, even though they provide short-term relief.

• Pathological Gambling (Gambling Addiction)
• Kleptomania (stealing)
• Pyromania (arson)

19. Adjustment Disorders - 18.9% (vs. 3%)¶

Adjustment disorders are described as reactions to a single or ongoing stressful life event.
Types of adjustment disorders include:

• Brief depressive reaction
• Prolonged depressive reaction (up to 2 years)
• Mixed anxiety and depressive reaction
• with a predominant impairment of other emotions
• with predominantly impaired social disorder
• with a combination of emotional and social disorders
• with other predominantly mentioned symptoms

Prevalence among individuals with ADHD:

• Among people with ADHD: 18.9%⁴¹
• for those not affected: 3.0%⁴¹
  = a 6-fold increase in risk

20. Intellectual disability - 1.4% to 13%¶

I was diagnosed with an intellectual disability along with ADHD

• at 13% ¹⁰⁴
• 1.4% for adults overall; 1.8% for women, 1.0% for men; ADHD-I 1.2%, ADHD-C 1.0%, ADHD-HI 5.0%⁶⁵

Among the 47,330 people with ADHD, the following were found:²³⁹

• 24.5% ASS
• 15.6% epilepsy
• 11.8% ADHD and learning disabilities
• 7.6% cerebral palsy
• 6.4% Down syndrome
• 1.0% other congenital syndromes

21. Eating Disorders – Loss of Control Eating Syndrome (LOC-ES) – 7.5 to 11.4% (vs. 1.4%)¶

A 12-fold increased risk among people with ADHD-HI.²⁴⁰²⁴¹

A cohort study of Iranian children and adolescents found an increased prevalence of ADHD—7.5%—among people with eating disorders.²⁴²

A very large study found that ADHD is associated with an 18.3-fold increased risk of bulimia or anorexia.²⁴³

Appetite disorders in adults with ADHD: 21%

Disordered eating was 40% more common among adolescents with ADHD.²⁴⁴

1.4% diagnostic prevalence of eating disorders among n = 221,714 people with ADHD (average age 25.1 years) ¹⁹

22. Psychoses - 8.8% (vs. 3%)¶

A study found that 8.8% of adults with ADHD had experienced psychosis at least once in their lives, compared with 3% of people without ADHD.⁶⁴

23. Epilepsy - 3.4% (vs. 0.5 to 1%)¶

A meta-analysis of 63 studies involving N = 1,073,188 participants from 17 countries found that:²⁴⁵
People with epilepsy had an ADHD prevalence of 22.3% (12.7% for ADHD-I).
People with ADHD had an epilepsy prevalence of 3.4%.
The prevalence of ADHD is significantly higher in patients with drug-resistant epilepsy.²⁴⁶

A study found that 35% of adults with epilepsy also had ADHD.²⁴⁷
Epilepsy and ADHD have a genetic correlation (rg = 0.18), which was even stronger in cases of focal epilepsy (rg = 0.23).²⁴⁸

Among adults with psychogenic non-epileptic seizures (PNES), 63.6% were found to have ADHD, while among adults with epileptic seizures (ES), 27.8% were found to have ADHD.²⁴⁹

Some medications used to treat seizures can cause or worsen ADHD symptoms as a side effect, while some ADHD medications can increase the risk of seizures.²⁵⁰

The prevalence of epilepsy in the general population is 0.5 to 1%.
44.1% of people with ADHD have at least one other mental health diagnosis at some point in their lives.²⁴⁸

24. Schizophrenia - 3.4% (vs. 0.8%)¶

Prevalence of Schizophrenia in ADHD:

• 4.59-fold increased risk of schizophrenia in individuals with ADHD (meta-analysis, k = 12, N = 1.85 million)²⁵¹
  • 5.09 times the risk of a psychotic disorder
• A 4.74-fold increased risk of schizophrenia in individuals diagnosed with ADHD in childhood²⁵²
  • 3.5% of the people with schizophrenia studied also had ADHD F 90.0, i.e., ADHD with hyperactivity, without ADHD-I (which, however, does not seem to fit in any way with the other figures mentioned in this section)
• A Norwegian cohort study found schizophrenia in 3.4% (men: 4.2%; women: 2.5%) of adults with ADHD, compared with 0.8% (men: 0.9%; women: 0.6%) of those without ADHD.⁵⁶
• Another study found a prevalence of schizophrenia among individuals with ADHD of 0.9% across the entire age range²⁷
• People with ADHD and an additional comorbidity had a 2.14-fold increased risk of schizophrenia compared to people with ADHD without any other comorbidities²⁵³. The risk of schizophrenia continued to rise with the number of comorbidities. In particular, ASD, intellectual disability, tic disorder, depression, and bipolar disorder showed the strongest correlation. 73.8% of people with ADHD who initially had no psychiatric comorbidities exhibited other psychiatric disorders prior to the onset of schizophrenia.

The prevalence of ADHD is significantly higher among people with schizophrenia.

• Children and adolescents with schizophrenia
  • 17% to 57% also have ADHD (meta-analysis, k = 5)²⁵⁴
• Adults with schizophrenia
  • 10% to 47% also have ADHD (meta-analysis, k = 5)²⁵⁴
• 47% reported having ADHD as a child or as an adult²⁵⁵
• 23% reported having ADHD during childhood and adulthood²⁵⁵

1.1% diagnostic prevalence of schizophrenia spectrum disorders among n = 221,714 people with ADHD (average age 25.1 years) ¹⁹

25. Obsessive-Compulsive Disorder - 1.9 to 2.4%¶

Obsessive-compulsive disorder is more commonly comorbid with ADHD in adults.⁶

• Total number of adults with ADHD: 1.9%; women 1.4%, men 2.4%; ADHD-I 0.9%, ADHD-C 1.5%, ADHD-HI 12.5%⁶⁵

• 2.4% across the entire age range²⁷

• A large study found that family members of people with ADHD had a 2.19-fold higher prevalence of ADHD.²⁵⁶

• Of 70 adults with ADHD, 8.7% had experienced an obsessive-compulsive disorder at some point in their lives, compared with 5.7% of the 70 adults without ADHD.⁵⁴

26. Migraine¶

Source²¹

27. Obesity¶

A 2.1-fold increased risk for people with ADHD.²⁵⁷

A study found that genetic variants associated with obesity may causally increase the risk of ADHD.¹⁵⁰
For treatment options, see section 4.5 below.

28. Socialization Disorder¶

Source⁶

29. Disorder of Sexual Development¶

Source⁶

• Earlier onset of sexual activity
  • for children with ADHD: 15 years²⁵⁸
  • for those not affected: 16 years²⁵⁸
• More sexual partners
  • for people with ADHD: 18.6²⁵⁸
  • for those not affected: 6.5²⁵⁸
• Less time with a partner²⁵⁸
• Higher rate of contraception²⁵⁸
• High rate of unwanted pregnancies
  • among children with ADHD: 38%²⁵⁸
  • Among those not affected: 4%²⁵⁸
    = 19.5 times the risk
• Teenage pregnancies: 5.5 times as many²⁵⁹
  • Teenage pregnancies among mothers with ADHD: 15.3%
  • Teenage pregnancies among mothers without ADHD: 2.8%
• Increase in the number of births (42:1)²⁵⁸
  = 42 times the risk
• Higher risk of sexually transmitted diseases
  • Among people with ADHD: 16%²⁵⁸
  • Among those not affected: 4%²⁵⁸
    = four times the risk

30. Narcolepsy¶

A meta-analysis found that approximately 33% of all people with narcolepsy also have ADHD.³⁸

31. Hoarding Disorder¶

Hoarding disorder is characterized by a strong urge to collect useless objects, leading to a tendency to clutter one’s living environment. A strong association with ADHD is being discussed.²⁶⁰ An overview of the literature can be found in Kuwano et al.²⁶¹ They found a comorbidity rate of ADHD among people with hoarding disorder of 26.7%.

In 71.6% of people with ADHD and comorbid hoarding, MPH improved the hoarding.²⁶² In 5%, it remained unchanged, and 23.4% showed a slight worsening.

32. Attachment Disorders¶

Source⁶

A study found that genetic variants associated with increased social interaction serve as a protective factor against ADHD.¹⁵⁰

33. Enuresis (Bedwetting)¶

Source⁶
Enuresis in children increased the risk of comorbid ADHD by a factor of 2.15 (OR 3.15).²⁶³

34. Encopresis (fecal incontinence)¶

Source⁶

35. Suicidal tendencies—2.4 to 6.7 times higher¶

A meta-analysis of 57 studies found a correlation between ADHD and²⁶⁴

• Suicide attempts (OR 2.37)
• Suicidal thoughts (OR 3.53)
• Suicidal thoughts (OR 4.54)
• a suicide (OR 6.69).

According to this, suicide is between 2.37 and 6.69 times more common among people with ADHD than among those without the condition.

Another study found an increased risk of suicide among children and adolescents with ADHD (OR 1.1); however, this risk was mediated by comorbid depression, irritability, and anxiety, not by ADHD itself.²⁶⁵

36. Fibromyalgia - 4-part series¶

A study found that the prevalence of ADHD was four times higher among people with fibromyalgia, without specifying the prevalence of fibromyalgia among people with ADHD.²⁶⁶

37. Dopamine Transporter Deficiency Syndrome (DTDS)¶

Dopamine Transporter Deficiency Syndrome (DTDS) is also known as infantile parkinsonism-dystonia.
Prevalence: very rare. To date, 60 people with ADHD have been reported.²⁶⁷

DTDS is an inherited genetic disorder characterized by a dysfunctional dopamine transporter.
Classic early-onset DTDS occurs within the first 6 months of life. In rare cases, late-onset DTDS may not become apparent until adolescence or even adulthood.²⁶⁷²⁶⁸

In one study, all people with early-onset (childhood or adolescent) parkinsonism showed severely impaired DAT function (homozygous for a dysfunctional variant or two heterozygous dysfunctional DAT variants). The more severe the DAT dysfunction, the earlier Parkinsonism developed. Most people with ADHD carried previously unknown de novo variants. The dysfunctions were diverse: reduced dopamine binding affinity, reduced cell surface transporter activity, loss of posttranslational glycosylation of the dopamine transporter, and failure of amphetamine-mediated dopamine efflux.²⁶⁸ The following DTDS-DAT variants were identified:

• Homozygous
  • c.941C>T → Ala314Val (3 out of 8 people with ADHD)
  • c.1269 + 1G>A → unknown (2 out of 8 people with ADHD); another study also reported this variant²⁶⁹
  • c.1408_1409delinsAG → Tyr470Ser (1 of 8 people with ADHD)
• Combination of two dysfunctional DAT variants:
  • 1 in 8 people with ADHD:
    • c.287-5_287-2delinsAAC → unknown
    • c.1156G>A –> Gly386Arg
  • 1 in 8 people with ADHD:
    • c.254G>T –> Arg85Leu
    • c.1333C>T –> Arg445Cys

Classic early-onset DTDS:²⁶⁷

• Onset within the first 6 months (infants)
• nonspecific symptoms
  • Irritability
  • Difficulties with breastfeeding
  • axial hypotension
  • delayed motor development
• followed by a hyperkinetic movement disorder
  • with characteristics of
    • Chorea
    • Dystonia
    • Ballism
    • orolingual dyskinesia
• Over time
  • Parkinsonism-Dystonia Complex
    • Bradykinesia, progressing to akinesia
    • dystonic posture
    • distal tremor
  • Rigidity
  • reduced facial expressions
  • severe motor delay due to impaired voluntary movements
  • Episodic dystonic status
  • Worsening of dystonia
  • secondary orthopedic, gastrointestinal, and respiratory complications
• intelligence is generally well preserved, with good cognitive development

Atypical late-onset DTDS:²⁶⁷

• Onset ranging from childhood through adulthood (fourth decade of life)
  • in 5 of the 60 people with ADHD
• Infancy and early childhood:
  • Normal psychomotor development
• Childhood
  • ADHD or individual ADHD symptoms
• late-onset
  • Parkinsonism-dystonia with
    • Tremor
    • progressive bradykinesia
    • variable tone
    • dystonic posture

Diagnostics:²⁶⁷

Cerebrospinal fluid (CSF) almost always shows

• HVA: The 5-HIAA ratio in SLC6A3-related DTDS is >4.0 (5.0–13.0) (normal range 1.0–4.0).
  • elevated levels of homovanillic acid (HVA, a metabolite derived from dopamine)
  • Normal levels of 5-hydroxyindoleacetic acid (5-HIAA, a metabolite derived from serotonin)
• Pterin: normal
• SPECT imaging using the ligand ioflupane (DaTSCAN):
  • highly abnormal results with absent or reduced tracer uptake in the basal ganglia
• Genetic analysis
  • Presence of a heterozygous, dominant-negative pathogenic SLC6A3 variant known to cause autosomal dominant DTDS
    • e.g., p.Lys619Asn

38. Stuttering¶

A study reports a 50% prevalence of ADHD among children and adolescents who stutter.²⁷⁰

39. Body-Focused Repetitive Behavioral Disorders (BFRDB, BFRB)¶

Body-focused repetitive behavior disorders (BFRDB) are related to impulse control disorders. Some of them are sometimes considered impulse control disorders, but distinguishing between the two is difficult.
BFRBDs are characterized by an irresistible urge, often accompanied by tension that is relieved by the act itself, which bears similarities to ICDs. While ICDs have traditionally been classified as distinct Disorders, BFRBDs are now classified in the ICD-11 within the spectrum of obsessive-compulsive disorders and related disorders, albeit in a separate subcategory, which underscores their complex nature.

The BFRDB includes, among other things:

• Bruxism (teeth grinding)
• Crepitus (cracking of the finger joints)
• Dermatophagia (skin biting)
• Thumb-sucking
• Lip-biting keratosis (lip biting)
• Morsicatio buccarum (cheek biting)
• Onychophagia (nail-biting)
• Onychotillomania (nail-biting)
• Rhinotillexomania (nose-picking)
• Trichophagia (eating hair)
• Trichotillomania (hair pulling)

39.1. Trichotillomania¶

Trichotillomania (compulsive hair pulling) was associated with a 5.34-fold increased risk of ADHD, as well as increased risks for²⁷¹

• Obsessive-compulsive disorder: 18.3 times
• Borderline personality disorder: 15 times
• Anxiety disorders: 10.2 times
• Alcohol abuse: 6.13 times
• Depression: 5.89 times
• Vitamin D deficiency: 4.2 times

39.2. Nail-biting¶

A study examined 450 children. 14% of them bit their nails. Among these were:²⁷²

• ADHD in 74.6%
• Oppositional defiant behavior in 36%
• Separation anxiety in 20.6%
• Bedwetting at 15.6%
• Tic disorders in 12.7%
• Obsessive-compulsive disorder in 11.1%
• intellectual disability in 9.5% of cases
• severe depressive disorders in 6.7%
• Pervasive developmental disorders in 3.2%

40. Mental Health Disorders Among Relatives of People with ADHD - 6.8 Times More Common¶

An analysis of the entire Taiwanese population in 2010 examined 220,966 parents of children with ADHD-HI (according to ICD-9, which did not recognize ADHD-I), 174,460 siblings of children with ADHD-HI, and 5,875 children of parents with ADHD-HI. Among these relatives of people with ADHD-HI, the risk of severe psychiatric disorders was significantly higher compared to matched control subjects who had no relatives with ADHD-HI:²⁷³

• ADHD-HI: 6.87 times the risk
• Autism spectrum disorder: 4.14 times the risk
• bipolar disorders: 2.21 times the risk
• Severe depressive disorders: 2.08-fold risk
• Schizophrenia: 1.69 times the risk

This can be interpreted as evidence of shared genetic causes. However, it is also theoretically conceivable that this could be explained by the immunological Consequences of (primarily viral) infections (which are more frequently transmitted among close contacts). See the chapter “ ” ⇒ The Immune System and Behavior.
Similarly, people who are close to one another are likely to share similar external life circumstances, as well as similar dysfunctional behavior patterns and stressful experiences. These mechanisms can reinforce one another.