Direct Effects of Cannabis Intoxication on Motivations for Softer and Harder Drug Use: An Experimental Approach to the Gateway Hypothesis.

This study experimentally tested whether there is a gateway-type effect of cannabis administration on tobacco and cocaine motivation and whether motivational responses predicted use 6 months later. A 2 (condition: active cannabis vs. placebo joint)×3 (substance stimulus type: tobacco, cannabis, and cocaine) factor within-subjects design for both implicit and explicit motivation. Both experimental sessions were conducted in a cannabis dispensary ("coffeeshop") in Amsterdam and were separated by ∼1 week, followed by a 6-month online follow-up. Eighty-five participants between 18 and 27 years of age (57% male), who used cannabis, tobacco, and cocaine <15 times per month, participated in session 1 (session 2: =79 and follow-up: =81). Counterbalanced over sessions, participants smoked an active and a placebo joint following a paced puffing procedure. Before and after smoking, craving and avoidance (explicit motivation) were assessed using visual analog scales, and after smoking, the stimulus response compatibility test was completed to assess approach biases (implicit motivation). Self-reported intoxication and similarity to their usual smoking experience were assessed at the end of both sessions. Self-reported frequency/quantity and dependence symptoms for tobacco, cannabis, and cocaine were assessed at all time points. A linear mixed model approach was used to assess the effects of condition, substance stimulus type, and their interactions on explicit and implicit motivation. In the active condition, participants reported higher levels of intoxication and an experience more similar to their usual smoking experience than in the placebo condition. There was no significant effect of condition, substance type, or their interaction on approach bias. Participants exhibited increased cannabis craving during the placebo condition only and increased explicit cannabis avoidance during the active condition only. Explicit tobacco avoidance decreased during both conditions. Baseline measures did not predict use at 6-month follow-up. In light users, cannabis intoxication did not affect implicit and explicit tobacco or cocaine motivations. Tobacco avoidance decreased regardless of condition, indicating that the cannabis cue-rich setting-rather than tetrahydrocannabinol itself-may momentarily increase the likelihood to smoke tobacco. However, motivation at baseline did not predict use 6 months later, deeming any gateway-like function unlikely.