Effects of expectancies on subjective responses to oral delta9-tetrahydrocannabinol.

The effects of expectancies on subjective responses to oral delta9-tetrahydrocannabinol (delta9-THC) were examined. Thirty-five regular marijuana users were assigned to one of two groups: one group was told that they may receive a cannabinoid or placebo and a second group was told that they may receive a drug from one of several classes of drugs (e.g., stimulant, sedative, antiemetic) or placebo. Regardless of the group to which they were assigned, subjects received each of two oral doses of delta9-THC (7.5 and 15 mg) and placebo, one dose per session, for a total of three sessions. Measures of subjective effects, including visual analog scales and the Addiction Research Center Inventory (ARCI), were administered at 0.5-h intervals throughout each session. Consistent with previous research using other drugs, subjects in the current experiment who expected to receive a cannabinoid reported greater pleasurable effects than subjects who did not have this expectancy. The results have implications for understanding the effects of cannabinoids when used in both recreational and clinical settings.