In an effort to further examine the results of a Swedish cohort study which found that heavy cannabis use at age 18 contributed to adult risk of schizophrenia, this study divided a sample of 759 participants into 3 groups. Group 1 consisted of 494 control subjects who reported never using cannabis at ages 15 and 18 or reported only using cannabis once or twice at these ages. Group 2 consisted of cannabis users who reported that at age 18 they used cannabis three times or more. Group 3 consisted of cannabis users who reported that at age 15 they used cannabis three times or more. These three groups were compared for psychiatric outcomes at age 26. Results of multiple linear regression and logistic regression analyses revealed that those who reported cannabis use at ages 15 and 18 experienced more schizophrenia symptoms by age 26 than the control group. After psychotic symptoms at age 11 were controlled for, the risk of adult schizophrenia symptoms remained higher among those who used cannabis at age 15; however, the risk was greatly reduced and was no longer significant. Cannabis use at age 15 did not predict depressive symptoms by age 26. The authors further concluded that earlier onset of cannabis use, at age 15 as opposed to age 18, conferred greater risk for schizophrenia symptoms, perhaps because those who began using cannabis at younger ages tended to become long-term users. The authors note that although a large population of adolescents use cannabis with few long term consequences, a vulnerable portion of the adolescent population risk harmful outcomes. It is recommended that policymakers and legislators focus prevention efforts on delaying the onset of cannabis use. References