A new study shows that in the time after first trying cannabis or first misusing prescription drugs, the percentages of young people who develop the corresponding substance use disorder are higher among adolescents (ages 12-17) than young adults (ages 18-25). In addition, 30% of young adults develop a heroin use disorder and 25% develop a methamphetamine use disorder a year after first using heroin or methamphetamine. These findings, published in JAMA Pediatrics, emphasize the vulnerability of young people to developing substance use disorders.