Although cannabis use has been associated with psychological and social
problems, there is no evidence that the practice actually causes such problems,
according to researchers from England and Switzerland (Lancet. 2004;363:1579-1588) .
The researchers reviewed 48 long-term studies that examined the association
between illicit drug use reported by adolescents and young adults and later
psychological or social problems. They found, based on an analysis of 16 studies
they judged to be of higher quality, that the data indicated that adolescents
who used marijuana were more likely than peers who did not use the drug to
have attained a lower educational level and use other illicit drugs, but that
it did not demonstrate a consistent association between marijuana use and
psychological or behavioral problems.
Stephenson J. Cannabis Consequences. JAMA. 2004;291(23):2809. doi:10.1001/jama.291.23.2809-b