Smoking marijuana as a teenager or young adult raises your risk of having psychotic symptoms later in life, a new Dutch study shows.

"This cements much more firmly the reality that marijuana use in adolescence is a risk factor, along with the other genetic, environmental and socioeconomic risk factors, for developing psychosis," said Dr. Kathryn Kotrla, associate dean and professor of psychiatry and behavioral sciences at the Texas A&M Health Science Center College of Medicine in Round Rock.

The findings, reported in the March 1 issue of the BMJ, come just weeks after Australian researchers reported on a connection between smoking marijuana and an onset of psychosis 2.7 years earlier than those who hadn't used the drug.

This latest study, led by Jim van Os from Maastricht University, seems to go one step further by showing that marijuana use actually precedes the onset of symptoms, suggesting a possible cause-and-effect relationship.

Some 16 million people in the United States alone use marijuana regularly, and most started smoking in their teens. It is the third most widely used addictive substance after tobacco and alcohol.

The researchers found that those who started smoking pot during the 10 years of the trial had double the risk of developing psychotic symptoms such as hallucinations, even after adjusting for factors such as age, sex, socioeconomic status, other drug use and other psychiatric diagnoses.

And the more persistent the use, the more persistent the symptoms.

Source: USA Today
http://www.usatoday.com/yourlife/health/2011-03-06-youth-use_N.htm