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Numerous studies have associated regular cannabis use with psychosis, but the causal relation is unclear. To explore this further, two research groups recently examined the effects of acute cannabis exposure.
On two separate occasions, Mason and colleagues gave intravenous Δ9-tetrahydrocannabinol (THC) or placebo to 22 healthy men who had no histories of psychiatric disorders or substance dependence. The men then answered mood and psychotic-symptom questionnaires and underwent cognitive testing. Compared with placebo, THC was associated with significant increases in psychotic symptoms (mainly ideas of reference), dysphoria, tiredness, and anxiety, and with impaired immediate recall and executive functioning. About 50% of participants had inc…