Several studies have suggested that marijuana use, particularly during adolescence, is related to acute psychotic episodes and future psychotic disorders, but little is known about whether adolescents who regularly use the drug over several years exhibit a systematic increase in their subclinical psychotic symptoms that persists during periods of sustained abstinence.
Researchers from University of Pittsburgh Medical Center and Arizona State University, Phoenix, analyzed data from a sample of 1,009 adolescent boys from Pittsburgh who self-reported annually on the number of days they used marijuana in the past year and experiences of subclinical psychotic symptoms (e.g., feelings of paranoia, hallucinations, bizarre thinking) from age 13 to 18. The teens also annually reported on the number of days they used alcohol, tobacco, and other illicit drugs.
As expected, substance use increased from age 13 to 18. By the last assessment, 270 participants reported having used marijuana weekly, 325 had used alcohol weekly, 377 had used tobacco daily, and 134 had used other illicit drugs at least once. For each year the participants engaged in weekly marijuana use, their expected level of subsequent subclinical psychotic symptoms rose by 21% and their expected odds of experiencing subsequent subclinical paranoia or hallucinations rose by 133% and 92%, respectively.
Additional analysis revealed that even when adolescents stopped using marijuana for one year, the effect of prior weekly marijuana use on total subclinical psychotic symptoms, paranoia, and hallucinations persisted. For each additional year adolescents engaged in weekly marijuana use, their expected number of total subclinical psychotic symptoms rose by 29% during subsequent periods of year-long abstinence, and their expected odds of experiencing paranoia and hallucinations rose by 112% and 158%, respectively.
“[T]he most concerning finding is that the effect of prior weekly marijuana use persists even after adolescents have stopped using for one year,” the researchers wrote.
While the authors acknowledged future studies are needed to determine whether the findings hold for girls and adults living in geographically diverse locales and whether the effect of regular adolescent marijuana use on subclinical psychotic symptoms persists into adulthood, they concluded, “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 seem to increase their risk of developing persistent subclinical psychotic symptoms.”
For related information, see the Psychiatric News article “Research Identifies Gene Linked to Cannabis-Induced Psychosis.”