New research is drawing a sharper line between teen marijuana use and long-term mental health risks. A study tracking 460,000 Northern California teens in the Kaiser Permanente system found those who used cannabis were significantly more likely to face serious psychiatric diagnoses by age 25. In fact, the risk of bipolar disorder and psychotic conditions like schizophrenia was about twice as high among teens who reported use in the past year. Researchers say the results underscore the importance of early intervention and honest conversations about cannabis and mental health.