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.
Researchers analyzed health data on 460,000 teenagers in the Kaiser Permanente Health System in Northern California. The teens were followed until they were 25 years old. 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.
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