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Ask the Mental Health Expert Archives 2001-2004

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Marijuana's Effects

Q. Recently, we had an attempted suicide in our community. It's being reported that it was a violent, psychotic reaction to marijuana. Is there such a thing? Is it common?

A. There is a mythos about cannabis/marijuana (MJ)--perhaps a romanticized remnant of the 60s--that MJ is a benign recreational drug that almost always mellows you out. Many people don't realize that the MJ out on the streets these days is a far more potent form than that available in the 60s; furthermore, MJ is sometimes laced with contaminants, such as PCP (angel dust) that can cause quite violent, psychotic behavior.

Several studies suggest that MJ may be implicated in both psychotic and violent episodes. For example, Thomas (Drug Alcohol Depend. 1996 Nov;42(3):201-7) studied a sample of 1000 New Zealanders aged 18-35 years were asked to complete a self-administered questionnaire on cannabis use and associated problems. Of those who responded, 22% reported acute anxiety or panic attacks following cannabis use. Fifteen percent reported psychotic symptoms following use. Most likely, psychosis in response to MJ is related to some underlying predisposition or vulnerability to psychosis (Verdoux et al, Psychol Med. 2003 Jan;33(1):23-32).

Regarding violence and MJ, Niveau & Dang (Med Sci Law. 2003 Apr;43(2):115-21) studied a series of 12 cases of violent crime, all committed under the influence of cannabis in Geneva, Switzerland, between 1996 and 2000. The study involved eleven males and one female, with a mean age of 26 years, who were using only MJ at the time they acted. Most subjects were chronic users, and ten had a past psychiatric history or personality disorder. Only three had been sentenced in the past for violent acts.

At the time of the aggression, all subjects exhibited adverse and acute effects related to MJ. All of them were judged by the court to be partially or totally non-responsible. The authors concluded that "?cannabis could have a specific role in the development of violent behavior patterns and that detection of its adverse effects should be systematic in criminal responsibility evaluation."

In short, while I doubt that violent psychotic or suicidal acts are commonly associated with MJ, such reactions may rarely be provoked in those with underlying psychiatric problems or predispositions.

December 2003

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