Frequent cannabis use poses risk of psychosis

Individuals who use cannabis weekly or more frequently appear to be at heightened risk of psychosis, as reported in a study.

Researchers conducted a systematic review and meta-analysis of available literature with the goal of identifying risk-thresholds between the frequency of cannabis use and psychosis development. They accessed multiple online databases and retrieved a total of 141 studies for full-text review. Of these studies, 10 were included in the meta-analysis.

The studies included a total of 7,390 participants with age ranging from 12 to 65 years. The primary outcome was first-episode psychosis in nine studies; one study had two primary outcomes, namely schizotypal signs and schizophrenia nuclear symptoms. The quality of included studies was assessed as moderate or high.

Pooled data revealed a marked log-linear dose–response association between cannabis use frequency and psychosis development. In a restricted cubic-splines model, the risk of psychosis significantly increased with weekly or more frequent cannabis use.

Compared with nonuse, weekly cannabis use was associated with a 35-percent risk increase (risk ratio [RR], 1.35, 95 percent confidence interval [CI], 1.19–1.52), while daily/near-daily use was associated with a 76-percent risk increase (RR, 1.76, 95 percent CI, 1.47–2.12).

Conversely, there were no significant increases in risk associated with monthly (RR, 1.10, 95 percent CI, 0.97–1.25) and yearly use (RR, 1.01, 95 percent CI, 0.93–1.11).

The present study may have important public health implications, such that prevention messages should convey the observed risk-thresholds.