This study is designed to investigate the associations among marijuana's discriminative stimulus, reinforcing, subjective (e.g. craving) and physiological effects, and to assess the relative ability of oral THC to block these effects.

Volunteers will be asked to live on a research unit for up to twenty-six (26) consecutive nights and will participate in a total of 38 study sessions held on 19 weekdays. Each session will last approximately four hours and there will be two sessions per day, therefore each study day will last approximately eight hours. In addition to these study sessions, an orientation session will be conducted on the Friday prior to admission to the inpatient unit, and a lottery session will be held on the last day of the study.

During each study session participants will be asked to smoke a cigarette. The cigarette may contain marijuana or it may contain placebo (a blank). Participants will also be asked to swallow a capsule 2-hours prior to smoking the cigarette. The capsule could contain placebo (a blank), THC (delta-9 tetrahydrocannabinol, which is the active ingredient in marijuana responsible for its mood effects), or d-amphetamine. We will have participants answer questions about how the drugs make them feel and measure their vitals signs (blood pressure, heart rate, and oxygen saturation) will be measured using a non-invasive (external) vitals monitor.

Inclusion Criteria:

• Female and male volunteers must be in generally good health (as indicated by results from medical history, physical exam, electrocardiogram, urine and blood samples at screening and upon arrival at the laboratory (urine samples only).
• Psychiatric examination must meet DSM-IV criteria for Cannabis Dependence.
• Individuals must be legally and mentally competent to provide written informed consent.
• Those who are unable to give their voluntary informed consent will not be accepted.

Exclusion Criteria:

• Current serious Axis I disorder (except Cannabis or Nicotine Dependence), neurologic, cardiovascular, pulmonary or systemic (e.g., renal, hepatic) disease; cognitive impairment; pregnancy (urine test), lactation (self-report), or not using (self-report) medically approved contraceptives.
• Applicants who express interest in treatment will not be accepted for study and will be provided with a treatment referral.

Marijuana dependent volunteers