A huge new study suggests teen cannabis use may double the risk of some of the most serious mental health disorders by young adulthood. Credit: Shutterstock Teenagers who use cannabis may be more likely to develop serious psychiatric conditions by young adulthood, according to a major new study published in JAMA Health Forum . Researchers tracked 463,396 adolescents between the ages of 13 and 17 through age 26. They found that teens who reported using cannabis within the previous year faced