Subjective Effects of Cannabis Before the First Psychotic Episode

Objective: The aim of the present study was to gain more insight into the positive and negative effects of cannabis in the prodromal phase of schizophrenia and in the ultra-high-risk (UHR) state for psychosis.

Method: A theory-driven questionnaire was used to examine subjective effects in the prodromal phase in male subjects with a recent onset of schizophrenia or related disorder (n = 52) and in the UHR state in help-seeking male subjects screened for being at UHR for psychosis (n = 17); both groups were compared to cannabis-using controls from the general population (n=52).

Results: Recent-onset patients and UHR subjects reported feeling more anxious, depressed and suspicious immediately after cannabis use. Some patients also reported feeling less depressed after cannabis use. Recent-onset patients reported increased visual and acoustic hallucinations, and confusion after cannabis use. Of the recent-onset patients 37% reported that their very first psychotic symptoms occurred during cannabis intoxication. Long-term effects of cannabis reported more often by both patient groups were depression, less control over thoughts and social problems.

Conclusions: These results suggest that schizophrenia patients in the prodromal phase and subjects at UHR for psychosis are more sensitive to some negative effects of cannabis, in particular psychotic effects, compared to cannabis users from the general population. Although limited by the retrospective design in the recent-onset patients, the present study adds qualitative evidence to longitudinal studies that suggest that cannabis is a component cause in the onset of the first psychotic episode. Further studies are needed on the objective and subjective effects of cannabis in UHR subjects.