Van Dam NT, Earleywine M, DiGiacomo G
Hum Psychopharmacol 2008 Aug;23(6):475-85
OBJECTIVE: To examine psychosis-like symptoms in users of legal and illicit drugs.
METHODS: Schizotypal Personality Questionnaire (SPQ) scores were compared in groups of people with different exposure to cannabis, with the use of other drugs serving as a covariate. Supplemental analyses compared users of legal and illicit drugs with cannabis use as a covariate.
RESULTS: Weekly (n = 111) and monthly (n = 136) cannabis users had higher scores on the SPQ than former (n = 143) and non-users (n = 81). The use of other drugs accounted for the links between cannabis and schizotypy. Lifetime use of psychomotor stimulant drugs plus ecstasy accounted for associations between cannabis and scores on the SPQ and its different subscales. Dividing groups by type of drug use revealed that those who used only cannabis and legal drugs (CLDs) (n = 126) were no different from those who used only legal drugs (LDs) (n = 74) but both groups scored significantly lower on the SPQ than polydrug users (n = 247). When controlling for marijuana use in the last month, the significant difference across drug use groups remained.
CONCLUSIONS: The results suggest that research on marijuana and schizotypy requires careful assessment of the use of other drugs, especially psychomotor stimulants and ecstasy.