Study of the Effects of MDMA/Ecstasy on Water Regulation, Sleep, and Cognition.

Inclusion Criteria: * Healthy men or women aged 18 to 50 years. * If female: abstains from heterosexual sex, not of childbearing potential, or reports using an approved contraceptive. * Experienced with MDMA * Fluent in English. * Willing and able to give written consent. * Healthy without medical contraindications to MDMA administration determined by the following: medical history, physical examination, 12-lead EKG, hematology, blood chemistry, and urinalysis. * Blood liver transaminase elevations up to 3 times the upper limit of normal. * If female: negative pregnancy test at screening and at the beginning of each hospital admission. * Negative urine drug test at screening and prior to each potential MDMA administration. Exclusion Criteria: * Current enrollment in a MDMA, alcohol, or other drug treatment program or current legal problems relating to MDMA, alcohol, or other drug use, including awaiting trial or supervision by a parole or probation officer. * Participants with a past-history of using only low doses of MDMA * Currently trying to quit MDMA use. * Current dependence on any other psychoactive drug (including nicotine). * Significant physical or psychiatric illness that might impair the ability to safely complete the study or that might be complicated by the study drugs, including prior seizures (after age 8) or other active neurological disease or clinically significant abnormalities on physical examination or screening laboratory values. * Likelihood of needing medications to treat an illness during the study period. * Body Mass Index \> 30 or \< 18. * HIV seropositive by self-report. * If female: pregnancy or lactation. * History of serious adverse event or hypersensitivity to MDMA. * Currently taking any medication other than over-the-counter non-steroidal anti-inflammatories, topical medications, inhaled asthma therapy, and over-the-counter non-sedating antihistamines. * Male neck size ≥ 17 inches, female neck size ≥ 16 inches * Modified Mallampati class ≥ 3. * Recent travel within 3 days to or from a different time zone, other than Mountain Standard Time. * Any other medical or psychosocial condition that would preclude useful, safe, or consistent participation.