Delta-9-tetrahydrocannabinol reduces willingness to exert effort in women.
The use of cannabis has been clinically associated with decreased motivation to engage in normally rewarding activities. However, evidence from previous controlled studies is mixed. In this study, we examined the effects of acute delta-9-tetrahydrocannabinol (THC) versus placebo on a task measuring willingness to exert effort for rewards. This is a secondary analysis of a larger study examining interactions between ovarian hormones and THC. In this within-subjects study, oral THC and placebo were administered under double-blind conditions in counterbalanced order to healthy young adult (M age 24 years) women with previous cannabis experience who were not regular users. Forty subjects completed three 4-h sessions with PL, 7.5 and 15 mg THC, while an additional 18 completed only PL and 15 mg THC sessions (design abridged due to pandemic). At each session, they completed a task consisting of making repeated choices between a hard and an easy task, which were worth varying amounts of money at varying probabilities. THC dose-dependently decreased hard task choices (drug effect, b - 0.79, SE 0.29, z - 2.67, p < 0.01), especially at moderate to high expected values of reward (drug × probability × amount interaction, b 0.77, SE 0.38, z 1.99, p 0.04). THC also slowed task performance (drug effect, b 0.01, SE 0.005, t(5.24) 2.11, p 0.04), but the effect of THC on choice was still significant after controlling for this psychomotor slowing. These findings support the idea that cannabis acutely reduces motivation to earn non-drug rewards. Still to be determined are the neurochemical mechanisms underlying this effect.