More evidence is required to associate cannabis use with negative psychosocial effects

The use of cannabis and other illicit drugs by young people is linked to psychosocial harm including psychological health problems, the use of other illegal drugs, reduced educational attainment, and antisocial behaviour. However, whether these associations are causal (ie, cannabis use is a direct cause of psychological illness and antisocial behaviour) remains unclear.

John Macleod from the University of Birmingham and colleagues reviewed general population longitudinal studies reporting associations between illicit drug use by young people and psychosocial harm. They identified 48 relevant studies, of which the most reliable evidence came from 16 studies.

In general, consistent associations were identified between cannabis use and both lower educational attainment and increased reported use of other illicit drugs. Less consistent associations were found between cannabis use and psychological health problems and problematic behaviour.

Dr Macleod, from the Department of Primary Care and General Practice comments: "We are not saying that currently available evidence suggests cannabis use is harmless.  Rather, we have found no strong evidence that use of cannabis in itself has important consequences for psychological or social health.  Problems with the available evidence render it equally unable to support this proposition. Better evidence is needed in relation to cannabis, which is widely used, and in relation to other drugs that, although less widely used, might have important effects".

For more information or a copy of the paper contact: Abigail Dixon, Press Officer, University of Birmingham; tel  +44 (0)121 414 5134; E) [email protected]
Or Richard Lane, The Lancet Press Office tel 0)20 7424 4949, E [email protected]