Daily use, especially of high-potency cannabis, drives the earlier onset of psychosis in cannabis users

Abstract

Cannabis use is associated with an earlier age of onset of psychosis (AOP). However, the reasons for this remain debated.

Methods: We applied a Cox proportional hazards model to 410 first-episode psychosis patients to investigate the association between gender, patterns of cannabis use, and AOP.

Results: Patients with a history of cannabis use presented with their first episode of psychosis at a younger age (mean years = 28.2, SD = 8.0; median years = 27.1) than those who never used cannabis (mean years = 31.4, SD = 9.9; median years = 30.0; hazard ratio [HR] = 1.42; 95% CI: 1.16-1.74; P < .001). This association remained significant after controlling for gender (HR = 1.39; 95% CI: 1.11-1.68; P < .001). Those who had started cannabis at age 15 or younger had an earlier onset of psychosis (mean years = 27.0, SD = 6.2; median years = 26.9) than those who had started after 15 years (mean years = 29.1, SD = 8.5; median years = 27.8; HR = 1.40; 95% CI: 1.06-1.84; P = .050). Importantly, subjects who had been using high-potency cannabis (skunk-type) every day had the earliest onset (mean years = 25.2, SD = 6.3; median years = 24.6) compared to never users among all the groups tested (HR = 1.99; 95% CI: 1.50- 2.65; P < .0001); these daily users of high-potency cannabis had an onset an average of 6 years earlier than that of non-cannabis users.

Conclusions: Daily use, especially of high-potency cannabis, drives the earlier onset of psychosis in cannabis users.

Keywords: age of onset; cannabis; drug use; gender; high-potency cannabis; psychotic disorders; survival plots.

Fig. 1.

This graph illustrates that cannabis use is associated with an earlier age of onset of psychosis in both males and females. Among those who never used cannabis, males are still younger than females when they experience their onset of psychosis. SD = standard deviation. As the age of onset is not normally distributed, we also report the median age in years (M = median).

Fig. 2.

Kaplan–Meier survival curves showing rate (y axis) of onset for participants grouped by age at first use of cannabis. Subjects who started using cannabis at age 15 years or younger experience their onset of psychosis (x axis in years) earlier compared with those who started using cannabis older than 15 years of age.

Fig. 3.

This graph illustrates that subjects who never used cannabis experience their first episode of psychosis at the oldest ages (mean ages in years) compared to those who used cannabis. In addition, the greater is the degree of exposure to cannabis (cannabis exposure scale expressed in type x frequency), the youngest is the mean age of onset of psychotic disorders. SD = standard deviation. As the age of onset is not normally distributed, we also report the median age in years (M = median).