Reinforcing effects of oral Δ9-THC in male marijuana smokers in a laboratory choice procedure

Rationale: Oral Delta-9-tetrahydrocannabinol (Delta(9)-THC; Marinol) is medically available for the treatment of nausea associated with cancer chemotherapy and for wasting syndromes related to HIV/AIDS. Little is known about its reinforcing effects. Objective: This study was conducted to characterize the reinforcing effects of oral Delta(9)-THC in experienced marijuana smokers under controlled laboratory conditions. Methods: Ten healthy male marijuana users completed this 17-day residential study. On days 2, 6, 10, and 14, at 0900 h, participants received a sample oral dose of Delta(9)-THC (0, 10, 20 mg) and an alternative reinforcer, a $2 voucher (redeemable for cash at study's end). Over the next 3 days, they had 11 opportunities to self-administer either the sampled dose of Delta(9)-THC or to receive a $2 voucher. Results: Participants chose active A(9)-THC (10 and 20 mg) more often than placebo (< two selections vs -four selections, respectively). However, they chose active Delta(9)-THC on less than 50% of choice opportunities. Both active A9-THC doses produced significant increases in positive subjective effects, impaired psychomotor performance, and increased heart rate, relative to the placebo conditions. Conclusion: These data indicate that oral A9-THC may have modest abuse liability in experienced marijuana smokers.