A huge study finds a link between cannabis use in teens and psychosis later

"As marijuana use among teens has grown in the past decade, researchers have been trying to better understand the health risks of the drug. Now, a new longitudinal study finds that cannabis use among adolescents increases risks of being diagnosed with bipolar and psychotic disorders, as well as anxiety and depression, years later. "This is very, very, very worrying," says psychiatrist Dr. Ryan Sultan at Columbia University, a cannabis researcher who wasn't involved in the new study published in the latest JAMA Health Forum."

"They found that the teens who reported using cannabis in the past year were at a higher risk of being diagnosed with several mental health conditions a few years later, compared to teens who didn't use cannabis. Teens who reported using cannabis had twice the risk of developing two serious mental illnesses: bipolar, which manifests as alternating episodes of depression and mania, and psychotic disorders, such as schizophrenia which involve a break with reality."

"The data included annual screenings for substance use and any mental health diagnoses from the health records. Researchers excluded the adolescents who had symptoms of mental illnesses before using cannabis. "We looked at kids using cannabis before they had any evidence of these psychiatric conditions and then followed them to understand if they were more likely or less likely to develop them," says Dr. Lynn Silver, a pediatrician and researcher at the Public Health Institute, and an author of the new study."

Health data on 460,000 teenagers in the Kaiser Permanente Health System in Northern California were analyzed and followed until age 25. Annual screenings for substance use and mental health diagnoses were recorded in health records. Adolescents with mental illness symptoms prior to cannabis use were excluded. Teens reporting cannabis use in the past year faced higher risks of later diagnoses of bipolar disorder, psychotic disorders, anxiety, and depression compared with nonusers. Cannabis users had about twice the risk of developing bipolar and psychotic disorders. About 4,000 teens were diagnosed with each of bipolar and psychotic disorders, both of which are highly disabling.

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