Marijuana use linked to psychosis

A very surprising meta-analysis was reported in the journal Nature. Apparently a group at Bristol University and Cardiff University, UK found that cannabis use was linked to much higher incidence of psychotic illness in later life. Apparently even the most minimal marijuana use increases the chance of psychosis by 41%. This is a meta-analysis that combines the results from 35 other studies, and which controls for intelligence, substance abuse of other kinds, and other factors. The result is particularly surprising since it is very much at odds with previous work, including a landmark study in the Lancet several years ago, but it looks at more extensive and perhaps more subtle data.

This does not show that there is necessarily a cause-and-effect relationship, just that there is a statistical connection. An established psychologist (my mother) suggested to me that the explanation is that people who are tending towards crazy will try just about anything, while those are are not cannot be predicted, which pretty much explains this correlation. [She really is a professor emeritus of psychology at the Universite de Montreal.]

I should note it has no personal bearing on any lifestyle choice I need to consider for myself; I am mentioning it only because of its broad significance.

References:

http://www.nature.com/news/2007/070723/full/070723-11.html [Nature.com]

The Lancet podcast on this work at http://podcast.thelancet.com/audio/lancet/2007/9584_28july.mp3 [ thelancet.com]