If your teenager uses cannabis, this large-scale study suggests the psychiatric risks are real and significant, particularly for psychosis and bipolar disorder during a critical window of brain development. A Kaiser Permanente-led study published in JAMA Health Forum followed over 463,000 adolescents aged 13 to 17 through age 26 and found that past-year cannabis use was associated with a doubled risk of developing psychotic and bipolar disorders. Cannabis use preceded psychiatric diagnoses by an average of 1.7 to 2.3 years, suggesting a temporal relationship between adolescent exposure and later psychiatric illness.