Marijuana use in adolescence may increase risk for psychotic symptoms

by Amanda Oldt

Regular marijuana use significantly increased risk for subclinical psychotic symptoms, particularly paranoia and hallucinations, among adolescent males. 

“Nearly all prior longitudinal studies examining the association between marijuana use and future psychotic symptoms have not controlled for recent patterns of use, have not repeatedly assessed marijuana use across adolescence, or have combined prior and recent use.

Therefore, it is impossible to delineate the enduring effect that regular use has on emergent psychotic symptoms and whether this effect is sustained when individuals remain abstinent for several months,” Jordan Bechtold, PhD, of University of Pittsburgh Medical Center, and colleagues wrote.

To determine associations between regular marijuana use in adolescence and subclinical psychotic symptoms, researchers evaluated 1,009 males from as early as first grade through age 18 years. Study participants were recruited in first and seventh grades.

Marijuana use, subclinical psychotic symptoms, and time-varying covariates such as other substance use and internalizing/externalizing problems were determined via self-reports from ages 13 to 18 years.

Analysis indicated that for each year adolescent boys engaged in regular marijuana use, their projected level of subsequent subclinical psychotic symptoms increased by 21% and projected risk for subclinical paranoia or hallucinations increased by 133% and 92%, respectively.

This effect persisted even when participants stopped using marijuana for 1 year.

Further, these associations remained after controlling for all time-stable and several time-varying covariates.

Researchers did not find evidence for reverse causation.

“This study demonstrates that adolescents are more likely to experience subclinical psychotic symptoms (particularly paranoia) during and after years of regular marijuana use.

Perhaps the most concerning finding is that the effect of prior weekly marijuana use persists even after adolescents have stopped using for 1 year,” the researchers wrote.

“Given the recent proliferation of marijuana legalization across the country, it will be important to enact preventive policies and programs to keep adolescents from engaging in regular marijuana use, as chronic use seems to increase their risk of developing persistent subclinical psychotic symptoms.”