Teenagers who have used cannabis in the past year have a dramatically higher risk of developing a psychotic disorder, according to a study published on Wednesday. The research, led by scientists from the University of Toronto, found that teenagers who used cannabis were 11 times more likely to develop a psychotic disorder compared to those who did not use the drug. When focusing on emergency room visits and hospitalizations, the risk increased to a staggering 27-fold for teens who had used cannabis.

Dr. Leslie Hulvershorn, a child psychiatrist and chair of the psychiatry department at Indiana University, emphasized the strong link between cannabis use and psychotic symptoms. “When I see youths with psychotic symptoms, they’re almost always using lots of cannabis,” Hulvershorn remarked. “It would be unusual to see someone present with psychotic symptoms to a hospital and not have smoked cannabis.”

This study contributes to the growing body of evidence that connects cannabis use to an increased risk of psychotic disorders, particularly during adolescence. Marijuana use, especially with high-potency products, has been associated with a range of mental health issues, including schizophrenia, anxiety, and depression.

“I think there’s enough evidence out there for us to recommend that teens probably shouldn’t be using cannabis,” stated the study’s lead author, Andre McDonald, a postdoctoral research fellow at McMaster University in Hamilton, Ontario. “If we can somehow ask teens to delay their use until their brain has developed further, it would be beneficial for public health.”

Although most teenagers who use cannabis will not develop psychotic disorders, McDonald stressed that the findings are worrisome given the severe impact these conditions can have. While the study does not definitively prove that marijuana causes psychotic disorders, the strong association suggests a significant correlation.

“The magnitude of the effect here is just hard to believe that it’s not related to cannabis,” Hulvershorn added.

Interestingly, the study found no link between cannabis use and psychotic disorders in individuals aged 20 to 33. Dr. Kevin Gray, a professor of psychiatry and director of addiction sciences at the Medical University of South Carolina, explained, “There’s something about that stage of brain development that we haven’t fully characterized — a window of time where cannabis use may increase the risk of psychosis. This study highlights the importance of delaying cannabis use until the 20s to mitigate serious risks.”

Published in the journal Psychological Medicine, the research analyzed data from over 11,000 teens and young adults aged 12 to 24 at the start of the study. The data was sourced from the Canadian Community Health Survey, focusing on the years 2009 to 2012. Participants were tracked for up to nine years to monitor any visits to doctors, emergency rooms, or hospital admissions related to psychotic disorders.

Of the teenagers who were hospitalized or visited emergency rooms for psychotic disorders, about five out of six had reported previous cannabis use. This finding underscores a critical developmental window during adolescence that is particularly high-risk for the onset of psychotic disorders linked to cannabis use.

The Biden administration is considering rescheduling marijuana from Schedule I to the less restrictive Schedule III, acknowledging its medical benefits at the federal level. This potential change is expected later this year. Currently, cannabis is legal for recreational use in 24 states.

Marijuana use among high school students has remained steady in recent years. Nearly one in three 12th graders reported using it in the past year, according to the 2023 Monitoring the Future Survey, which tracks drug and alcohol use among adolescent students nationwide.

The study did not specifically examine how the potency of marijuana products affected the risk of mental disorders. However, previous research has indicated that higher potency marijuana is linked to a greater risk of developing psychotic symptoms. The endocannabinoid system, a complex signaling system in the brain targeted by marijuana, might be particularly susceptible to disruption during adolescence, leading to symptoms such as hallucinations and difficulty distinguishing reality from internal experiences.

In conclusion, this study highlights the critical need for public health recommendations to delay cannabis use until after the adolescent brain has fully developed, potentially reducing the risk of serious mental health disorders.