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Substance Abuse and Addiction Health Center

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Federal Report: Marijuana Causes Mental Illness

But Critics Say Politics Is Driving Premature Conclusions About Drug's Role


"The evidence is collectively indicating that there is a causal connection," says Neil McKeganey, PhD, professor of drug misuse at the University of Glasgow in Scotland.

McKeganey notes that scientists have not yet uncovered evidence linking marijuana use to the brain changes routinely seen in people who suffer from mental illness. "If we wait until we understand that mechanism, we will lose thousands of young people," he says.

But Paul P. Casadonte, MD, a psychiatrist and associate clinical professor at New York University, cautions in an interview that research is not yet strong enough to show a causal link between marijuana use and serious mental disorders. He suggests that such claims by Walters and other administration officials were intended to further the Bush administration's efforts to quell young peoples' marijuana use.

"That's dangerous territory. It's politics more than science at this point," says Casadonte, who is also director of substance abuse treatment programs at New York Department of Veterans Affairs Medical Center.

Casadonte warns that Tuesday's study of early marijuana use does not necessarily prove that smoking at a young age leads directly to later illness. "We do know that the younger you start, the more likely that there's something mentally wrong with you to begin with. Marijuana has more of an addiction potential than most people want to believe," he says. "But basically we just don't have the science" to claim a causal link with mental illness.

Federal officials remain alarmed at high rates of marijuana use in younger and younger U.S. children. According to the NIDA, marijuana is the most commonly used illicit drug in the U.S.; nearly 53% of Americans who say they've used the drug say they tried it for the first time before age 17.

According to data from the CDC, one-tenth of students nationwide had tried marijuana for the first time before age 13. Overall, the rates were higher in males (13%) than in females (6%).

Officials are preparing to launch a national campaign using newspaper and magazine advertisements to draw parents' attention to a link between marijuana use and mental illness.

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