Goals: (1) Determine the lowest single dose of oral rimonabant that elicits measurable cannabinoid withdrawal. (2) Characterize cognitive performance, subjective state, physiological condition, and regional brain activation (measured by functional magnetic resonance imaging [fMRI]) during acute and chronic administration of oral delta 9-tetrahydrocannabinol (THC) and during cannabis withdrawal. (3) Characterize the pharmacokinetics of oral THC and metabolites in body fluids and hair and of rimonabant in plasma.