Researchers at Prince of Wales Hospital, in New South Wales, Australia, reviewed the evidence to determine the extent to which use of cannabis, alcohol, and other psychoactive substances affect the age at onset of psychosis.

First, the details.

  • There were 83 studies of 8167 substance-using patients.

And, the results.

  • A meta-analysis of the data revealed that the age at onset of psychosis for cannabis users was about 3 years younger than for nonusers.
  • For those with broadly defined substance use, the age at onset of psychosis was 2 years younger than for nonusers.
  • Alcohol use was not associated with a significantly earlier age at onset of psychosis.

The bottom line?

The authors concluded, “The results of meta-analysis provide evidence for a relationship between cannabis use and earlier onset of psychotic illness, and they support the hypothesis that cannabis use plays a causal role in the development of psychosis in some patients.”

The results suggest the need for renewed warnings about the potentially harmful effects of cannabis.

2/12/11 20:37 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.