[Cannabis abuse in patients with psychiatric disorders: an update to old evidence]

To perform an update on cannabis abuse by patients with psychiatric disorders.

A search was performed in the electronic databases Medline, The Cochrane Library Database, Lilacs, PubMed, and SciELO, using the keywords 'marijuana abuse', 'cannabis abuse', 'psychiatric disorders', and 'mental disorders'. Articles published until December 2009, dealing with cannabis abuse and dependence in association with other psychiatric disorders were included.

Cannabis abuse was found to be associated with increased risk for the onset of schizophrenia and chronic psychotic symptoms, although these findings require confirmation from additional research. Cannabis seems to be one of the drugs of choice of individuals with bipolar disorder, despite evidence that manic states can be induced by its use. Cannabis abuse also occurs frequently in individuals with anxiety disorders, but the relationship between the chronic nature of these conditions and the use of marijuana remains uncertain. In respect to depression, there is no clear evidence to date that depressive patients use cannabis as a form of self-medication. In individuals with psychiatric disorders, the use of cannabis has been associated with increased positive symptoms, additional negative symptoms in the course of illness, impaired treatment compliance, and more hospitalizations.

The abuse of cannabis by patients with psychiatric disorders such as schizophrenia and mood and anxious disorders has a negative impact both in the acute and advanced stages of these conditions, although further investigation on this association is still necessary.