Effects of a Range of Naltrexone Doses in Combination With Smoked Marijuana

Inclusion Criteria: * Current marijuana use * Able to perform study procedures * 21-45 years of age * Women practicing an effective form of birth control Exclusion Criteria: * Current, repeated illicit drug use (other than marijuana) * Presence of significant medical illness (e.g., diabetes, cardiovascular disease, hypertension, examination, laboratory hepatitis, clinically significant laboratory abnormalities, tests, 12-lead ECG, Mantoux test LFTs \> 3x upper limit of normal) * History of heart disease * Request for drug treatment * Current parole or probation * Pregnancy or current lactation * Recent history of significant violent behavior * Previous adverse reaction to naltrexone * Major current Axis I psychopathology Psychiatric interview (e.g., major depressive disorder, bipolar disorder, suicide risk, schizophrenia) * Current use of any prescription or over-the-counter medication