We sought to examine the relation between cannabis abuse and the symptomatic course of recent-onset schizophrenia and related disorders.
A prospective cohort study over a year using monthly Brief Psychiatric Rating Scale assessments.
Cannabis-abusing patients (n=24) were compared with nonabusers (n=69). Eleven patients were mild and 13 were heavy cannabis-abusing patients.
Significantly more and earlier psychotic relapses occurred in the cannabis-abusing group (P=.03). This association became stronger when mild and heavy cannabis abuse were distinguished (P=.002). No confounding effect of other variables, eg, other street drugs, was found. In all but one patient, cannabis abuse preceded the onset of the first psychotic symptoms for at least 1 year.
Cannabis abuse and particularly heavy abuse can be considered a stressor eliciting relapse in patients with schizophrenia and related disorders and possibly a premorbid precipitant.