The primary aim of the present research project is to examine the feasibility, as measured by treatment perceptions, and tolerability, as measured by adherence and attrition, of two weeks of flashed light therapy alone followed by four weeks of daily flashed light therapy combined with four weekly videoconference-delivered cognitive behavioral therapy sessions targeting circadian rhythms and sleep in four adolescents aged 14 to 17 years with attention-deficit/hyperactivity disorder and delayed sleep-wake schedules.

Participation in this research will last about 7 weeks. Participation will involve an initial screening visit lasting 3 hours to assess eligibility. This visit will involve interviews and tasks to assess for psychiatric diagnosis, sleep history, ADHD severity, and thought patterns. Participants and parents will also complete questionnaires assessing parent-reported and self-reported ADHD severity, personal and family demographics, and medical and psychiatric history. Following this visit, participants will be asked to monitor their sleep for 7 nights using a sleep watch and sleep diary, and provide daily report of bedtimes and risetimes via text message.

After sleep monitoring, an 8-hour baseline assessment visit involving interviews, questionnaires, and saliva sampling will be scheduled from 7 hours before average habitual bedtime up until average bedtime to assess the internal body clock. The morning following the baseline assessment, light therapy will begin and continue daily for two weeks. During the two-week period, participants will monitor sleep nightly using a sleep watch and sleep diary.

Following termination of the two-week course of flashed light therapy, participants will complete an 8-hour mid-treatment assessment involving interviews, questionnaires, and saliva sampling, as described above. Following this assessment, participants will begin weekly 50-minute individual videoconference-delivered cognitive behavioral therapy while continuing to use the flashed light therapy device and monitor sleep (via sleep diary, watch, and sleep location verification) for a duration of four weeks. Following treatment, participants will have a post-treatment 8-hour assessment, again involving interviews, questionnaires, and a salivary assessment of the internal body clock, as described above.

Inclusion Criteria:

1. Age of 14 to 17 years
2. Current DSM-5 diagnosis of attention-deficit/hyperactivity disorder (any type)
3. Self-reported average bedtime of 11:00 pm or later, with difficulty shifting bedtime earlier and difficulty waking up early enough in the morning
4. Evening chronotype (i.e., score ≤ 27 on the Morningness-Eveningness scale for Children)
5. Clinically significant ADHD severity (ADHD-Rating Scale-5 score ≥ 24)
6. Moderate global functioning impairment or worse (Clinical Global Impression-Severity scale score ≥ 4)
7. Attending school (i.e., standard school year or summer school) during study enrollment
8. Fluency in English

Exclusion Criteria:

1. Current or lifetime diagnosis of bipolar Disorder, psychosis, autism spectrum disorder, or pervasive developmental disorder
2. Alcohol or substance dependence or suicidality within the past 6 months
3. Current depression or anxiety in the severe range or higher
4. Sleep disorder present besides delayed sleep-wake phase disorder (Clinical Sleep History Interview)
5. Sleep solely in the prone position (i.e., on stomach)
6. Full scale IQ ≤ 80 (Wechsler Abbreviated Scale for Intelligence-II)
7. Use of any over-the-counter (e.g., melatonin, Benadryl) or prescribed sleep medication in the past month or planned use during the study
8. Changes to any psychiatric medication within one month of study enrollment or planned changes during the study
9. Use of photosensitizing medication within one month of study enrollment or planned during the study
10. Participation in behavior therapy for sleep and/or ADHD within 3 months of study enrollment or planned participation during the course of the study
11. Use of light therapy within 6 months of study enrollment or planned use during the study
12. Travel across > 2 time zones within one month of study enrollment or planned travel outside of the time zone of participation during the study
13. Structural barriers to sleep (e.g., night shift work, extracurriculars scheduled until late in the evening, early rising for sports practice)
14. Medical or neurological condition (e.g., seizure disorder, chronic migraines) that would interfere in the individual's ability to participate