Light therapy
A very small study with n = 29 adults found positive effects of early morning light therapy in the fall/winter months on objective and subjective ADHD symptoms, mood and a shift in the circadian rhythm.1 The shift in the circadian rhythm appeared to have the greatest influence on the improvement of ADHD symptoms. Another, even smaller study on 16 adults came to similar conclusions.2
A third placebo-controlled study comparing the circadian rhythm with melatonin or melatonin plus light therapy also found that light therapy (here: as an addition to treatment with melatonin) could shift the circadian rhythm forward and that this had positive effects on ADHD symptoms. Melatonin alone had a stronger effect than light therapy, light therapy improved the result of melatonin treatment.3
A review confirmed these results.4
Rybak, McNeely, Mackenzie, Jain, Levitan (2006): An open trial of light therapy in adult attention-deficit/hyperactivity disorder. J Clin Psychiatry. 2006 Oct;67(10):1527-35. doi: 10.4088/jcp.v67n1006. PMID: 17107243. n = 29 ↥
Fargason, Fobian, Hablitz, Paul, White, Cropsey, Gamble (2017): Correcting delayed circadian phase with bright light therapy predicts improvement in ADHD symptoms: A pilot study. J Psychiatr Res. 2017 Aug;91:105-110. doi: 10.1016/j.jpsychires.2017.03.004. PMID: 28327443. n = 16 ↥
van Andel, Bijlenga, Vogel, Beekman, Kooij (2020): Effects of chronotherapy on circadian rhythm and ADHD symptoms in adults with attention-deficit/hyperactivity disorder and delayed sleep phase syndrome: a randomized clinical trial. Chronobiol Int. 2020 Oct 29:1-10. doi: 10.1080/07420528.2020.1835943. PMID: 33121289. n = 51 ↥
Snitselaar, Smits, van der Heijden, Spijker (2017): Sleep and Circadian Rhythmicity in Adult ADHD and the Effect of Stimulants. J Atten Disord. 2017 Jan;21(1):14-26. doi: 10.1177/1087054713479663. PMID: 23509113. REVIEW ↥