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

List the inclusion criteria: * Age 18-25 years * Physically and psychiatrically healthy, as determined by instruments described below * 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 engaging in daily or near-daily cannabis use during the past year. 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 List the 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 hea…