The Pharmaceutical Journal
Vol 269 No 7226 p768
30 November 2002

This article
Reprint
Photocopy

News summary

Related websites
BMJ (bmj.com)

Cannabis use by teenagers raises risks of mental health problems

Cannabis use during adolescence appears to increase the risk of developing schizophrenia, depression and anxiety in later life.

In the first of three studies published in the BMJ (2002;325:1195), Australian researchers found that young women were over five times more likely to report depression and anxiety if they used cannabis daily (odds ratio 5.6, 95 per cent confidence interval 2.6–12). In addition, teenagers using cannabis weekly had just over twice the risk (2.3, 1.3–4.2). The researchers comment that depression and anxiety in teenagers do not predict later cannabis use, indicating that taking cannabis to overcome these is unlikely to be the reason for the association.

In the second study (Ibid, p1199), cannabis was associated with a dose-dependent increased risk of schizophrenia that was not explained by personality traits or use of other psychoactive drugs. The researchers analysed data from over 50,000 Swedish conscripts. After adjusting for a variety of factors, including poor social integration and cigarette smoking, they found that those who had used cannabis on more than 50 occasions were three times more likely to develop schizophrenia than those who had never used the drug (3.1, 1.7–5.5).

Meanwhile, a prospective study of 1,000 young New Zealanders found that those who had used the drug by the time they were 15 years of age were more than four times as likely to be diagnosed with schizophrenia in adulthood than controls (odds ratio 4.5, P=0.035). However, after adjusting the data for psychotic symptoms identified at age 11, the researchers found the risk was reduced by 31 per cent and was no longer statistically significant (Ibid, p1212). They say that although most young people who use cannabis in adolescence do so without harm, there is a vulnerable minority that suffer harmful outcomes. "Cannabis use among psychologically vulnerable adolescents should be strongly discouraged," they conclude.

An accompanying editorial says that the dose-response relationships shown for schizophrenia and depression highlight the importance of decreasing cannabis use.