By Steven Reinberg
Friday, July 27, 2007 12:00 AM
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 ofThe 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."
One expert believes the link between marijuana and the risk for psychosis is real, and needs to be viewed as a problem much like tobacco and its health risks.
"This seems to be the best of studies conducted so far, and although this issue could never be proven directly, due to ethical limitations of a prospective exposure study, it provides a solid evidence that smoking cannabis increases risk for the development of psychosis later in life," said Dr. Adam Bisaga, an associate professor of clinical psychiatry in the Department of Psychiatry, Division on Substance Abuse, at Columbia University College of Physicians and Surgeons, in New York City.
The study should change the view of risks involved in smoking cannabis, which until now has been considered by many to be a relatively benign substance, with low addiction potential and few long-term risks, Bisaga said.
"We should change our approach and screen for cannabis use in the primary-care setting, counsel those who use it about increased risk of developing a potentially devastating psychotic illness and recommend stopping smoking," Bisaga said. "For those that are not able to stop using because of cannabis addiction, we should refer them to treatment."
Cannabis addiction can be effectively treated, which may reduce the risk of psychosis, Bisaga said.
"It appears that we are repeating the process we went through with tobacco use, initially considered to be benign, but as long-term risks were recognized, societal attitudes have changed, effective prevention strategies and treatments were developed, and rates of use and associated risks have diminished," he said. "We should now think about adopting some of these strategies to help cannabis smokers."
To learn more about drug addiction, try the U.S. National Institute on Drug Abuse.
SOURCES: Stanley Zammit, clinical lecturer, psychiatric epidemiology, Cardiff University, U.K.; Adam Bisaga, M.D., associate professor, clinical psychiatry, Department of Psychiatry, Division on Substance Abuse; Columbia University College of Physicians and Surgeons, New York City; July 28, 2007,The Lancet