Pot Ups Risk for Mental Illness

The more you smoke, the greater the odds, researchers report.

By Steven Reinberg
HealthDay Reporter
Friday, July 27, 2007; 12:00 AM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

THURSDAY, July 26 (HealthDay News) -- Smoking marijuana can raise your risk of developing a psychotic illness by 40 percent, British researchers say.

Marijuana is the most commonly used illegal substance in most countries, including the United States. In fact, some 20 percent of young people report using it at least once a week or more, according to the article in the July 28 issue of The Lancet.

"People who used cannabis had a greater risk of developing psychotic outcome then people who didn't use cannabis," said study author Stanley Zammit, a clinical lecturer in psychiatric epidemiology at Cardiff University.

In the study, Zammit's group analyzed 35 studies that looked at whether marijuana was linked to mental health disorders.

They found that people who had used marijuana were 41 percent more likely to have a psychosis compared with people who had never used the drug. They also found that the risk increased as the amount of marijuana used and the length of time someone used the drug increased.

Those who smoked the most marijuana had a twofold to threefold increase in the risk of developing a psychotic problem, Zammit said.

Part of the explanation for this effect is that people who use marijuana are at higher risk for mental problems even without the drug, Zammit explained. "Nevertheless, even when these factors were adjusted for, there still remained an association between marijuana and psychosis, which suggests that there is a causal relationship there," he added.

Recent estimates are that 40 percent of young adults and adolescents have used marijuana at some time in their lives, the researchers noted.

"People who are thinking about using cannabis or are already using cannabis need to be made aware of this risk," Zammit said. "People who experience any problems when using cannabis -- say if they become anxious or paranoid when they use cannabis -- those are warning signs, and people should be aware that they ought to be considering either stopping use or cutting down how often they use or the amount of cannabis they use."