Cannabis Effects on Sleep, Circadian Rhythms, and Light Sensitivity in Young Adults

The goal of this study is to learn how cannabis use and discontinuation affect sleep, circadian rhythms, and sensitivity to light. The main questions it aims to answer are:

1. Does cannabis use and discontinuation impact sleep drive?
2. Does cannabis use and discontinuation impact light sensitivity and circadian phase?

Researchers will compare sleep, circadian phase, and light sensitivity within regular cannabis users before, during, and after a cannabis discontinuation protocol; researchers will also compare sleep, circadian phase, and light sensitivity between regular cannabis users and control non-cannabis users.

Participants will:

1. Participate in a 1-week baseline period consisting of at-home monitoring (sleep diaries, actigraphy, EEG headband).
2. Participate in a 2-night lab visit consisting of circadian phase and light sensitivity assessment.
3. Participate in a 4-week cannabis discontinuation protocol (cannabis users only).
4. Participate in a second 2-night lab visit after the discontinuation protocol (cannabis users only).

Eligibility Criteria:
Inclusion Criteria:

* Age 18-25 years
* Physically and psychiatrically healthy
* Cannabis-Using group only: Regular cannabis use, defined as "frequent" (6-29 days/month) or "daily" (daily) use over the past 3 months
* Cannabis-Using group only: Willingness to discontinue cannabis for 4 weeks.
* Control group only: No cannabis use in the past 3 months. Deny lifetime history of engaging in daily or near-daily cannabis use over any month-long period. No history of alcohol and/or substance use disorders. No current sleep disorders (including insomnia and delayed sleep phase disorder).
* Provision of written informed consent

Exclusion Criteria:

* Significant or unstable acute or chronic medical conditions. Examples of such conditions include, but are not limited to, central nervous system disorders (e.g., head injury, seizure disorder, multiple sclerosis, tumor), cardiovascular or hemodynamically significant cardiac disease, liver disease (e.g., acute or chronic hepatitis, hepatic insufficiency), migraine or chronic headaches, active peptic ulcer disease, inflammatory bowel disease, renal failure, arthritis, and diabetes and other endocrine disorders. Seizure disorder in particular will be exclusionary due to the increased risk it confers for cannabis withdrawal symptoms. Eye/retinal conditions such as diabetic retinopathy or glaucoma will be exclusionary, although should be very rare in this population. Individuals with well-controlled health conditions that do not affect sleep, retinal function, and/or well-being (e.g., well-controlled thyroid disorders, asthma, or ulcer) will not be excluded. To evaluate these criteria, potential participants will complete a locally-developed Medical History Questionnaire.
* Past or current DSM-5 bipolar disorder or psychotic disorders. Psychiatric disorders will be evaluated using the Mini International Neuropsychiatric Interview (MINI), supplemented by clinical interview and the WHO-DAS 2.0. Researchers will not exclude participants for subsyndromal symptoms or disorders in these domains. Researchers will not exclude participants for other psychiatric disorders, particularly given the high comorbidity between cannabis use disorder and major depression and anxiety disorder, long as severity is in the moderate range or lower based on the WHO-DAS 2.0 (average score \&lt;4).
* Daily use of alcohol; regular use of illicit substances. Regular use (as defined above) of illicit substances other than cannabis over the past 3 months will be exclusionary. Substance use will be assessed using the Timeline Follow Back method, as well as a urine drug screen.
* Past or current substance use disorders other than cannabis use disorder and nicotine use disorder.
* Current syndromal sleep disorders other than insomnia and delayed sleep phase disorder, including narcolepsy, restless legs syndrome, obstructive sleep apnea, and current night shift work (i.e., any work occurring between the hours of midnight and 6:00 a.m.). Researchers will not exclude for subsyndromal symptoms or disorders in these domains. Researchers will not exclude Cannabis-using participants for insomnia and delayed sleep phase disorder because of their conceptual overlap and high co-occurrence with sleep phenotypes of interest. Sleep disorders will be diagnosed according to criteria in the DSM-5 and the International Classification of Sleep Disorders, 3rd Edition, 2014. These disorders will be evaluated using clinical interview and the Structured Clinical Interview for Sleep Disorders, Revised Version (SCISD-R). Control participants will be excluded for any current sleep disorders, including insomnia and delayed sleep phase disorder.
* Travel across 2+ time zones in the past 60 days.
* Benzodiazepines and non-benzodiazepine hypnotic drugs ("Z-drugs"). Other sleep- promoting medications will be permitted, including SSRIs/SSNIs, will be permitted if on stable dose and not in the acute phase of treatment. In order to evaluate medications, participants will complete a listing of current medications, including prescription and over the counter medications, "natural" preparations, and nutritional supplements.