Generation Next Blog
Smoking pot can lead to mental health issues
Many people, including regular cannabis users, argue that there is no link between using cannabis and the onset of mental health issues later in life. However a longitudinal study spanning 10 years has now shown that new users of cannabis, especially young people, are more likely to develop psychotic symptoms than those who never used cannabis.
Researchers took data from a 10-year, prospective population-based cohort study on the early developmental stages of psychopathology. Their age ranged between 14 and 24 years old.
All participants gave information about substance use and completed a diagnostic mental health interview at the beginning of the study and at three follow-up assessments during the course of the 10 years, including after 1.6 years, 3.5 years and again after 8.4 years. Cannabis use was defined as having used cannabis five times or more.
In analysis that adjusted for demographic factors, use of other drugs, childhood trauma, and urban/rural environment and that excluded individuals who reported using cannabis before the study or who had pre-existing psychotic symptoms.
The study found that young people who only began to use cannabis after the study began and up to the 3.5-year follow-up were almost twice as likely as nonusers to report psychotic experiences at the 8.4-year follow-up (odds ratio, 1.9; 95% confidence interval, 1.1–3.1).
Continued cannabis use (reported use at baseline and 3.5-year follow-up) increased the risk for persistence of psychotic symptoms between the 3.5 and 8.4 year follow-up.
This study adds to a number of carefully controlled, longitudinal studies demonstrating a link between cannabis use in adolescence and the emergence of psychotic symptoms or other adverse mental health outcomes over time.
Some, but not all, of these studies suggest that cannabis use before age 16 years confers the greatest risk.
Although use of alcohol and tobacco poses far greater harm to adolescents, young adults, and society than does cannabis use, this study reminds us that adolescent use of marijuana cannot be considered a harmless rite of passage.
Writer Helen Splarn. Editor Dr Ramesh Manocha.
Source: Kuepper R et al. Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study. BMJ 2011 Mar 1; 342:d738. (http://dx.doi.org/10.1136/bmj.d738)