Adolescent cannabis users are neither more resilient nor more vulnerable than adult cannabis users to the acute psychotomimetic, verbal memory-impairing, or subjective effects of cannabis. In a randomized, double-blind, placebo-controlled crossover experiment with 24 adolescents (16-17 years old) and 24 adults (26-29 years old) who used cannabis 0.5-3 days per week, vaporized THC (8 mg for a 75 kg person) and THC plus CBD (24 mg) both significantly increased subjective drug effect, impaired verbal episodic memory, and increased psychotomimetic effects compared to placebo. There was no evidence that adolescents differed from adults in their responses, and CBD did not modulate the acute effects of THC.
Regular cannabis users show no overall difference from non-users in how they update their beliefs under uncertainty, a cognitive process linked to psychosis. Both groups correctly adjusted their confidence and learning when uncertainty changed. However, among cannabis users, those who used cannabis more frequently performed worse on the task than less frequent users. This pattern resembles the abnormal belief-updating seen in psychosis, suggesting that frequent cannabis use may share a cognitive risk marker with psychosis, even though cannabis use status alone does not impair this process.