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Substance Abuse and Addiction Health Center

Federal Report: Marijuana Causes Mental Illness

But Critics Say Politics Is Driving Premature Conclusions About Drug's Role
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May 3, 2005 -- Children who use marijuana before age 12 are twice as likely to later develop serious mental illness as those who don't try the drug until they're 18, according to a federal report released Tuesday.

Bush administration officials pointed to the study as growing evidence that smoking marijuana may cause mental illnesses -- including depression, schizophrenia, and suicide attempts -- in some people.

But while the association of drug abuse and addiction with mental illness is well known, a causal connection between marijuana smoking and psychiatric disorders is not clear, other experts say.

In Tuesday's study, 21% of people who reported first using marijuana before age 12 also reported that they later went on to develop signs or symptoms of a serious mental illness. Those who said they used the drug only after age 18 had a 10.5% chance of reporting similar problems.

The study was based on federal drug use data culled in 2002 and 2003. Other past studies publicized by federal officials Tuesday also point to a connection between marijuana use and the development of mental problems later on.

"New research being conducted here and abroad illustrates that marijuana use, particularly during the teen years, can lead to depression, thoughts of suicide, and schizophrenia," said White House Drug Czar John P. Walters. "This press conference is a public health warning."

Another study highlighted by officials, published in 2001, suggested that people who were not depressed but used marijuana were four times more likely to develop depression years later than those who never used the drug.

Researchers have long observed a connection between drug use and mental illness. Many studies show the simultaneous occurrence of mental illness and substance abuse. People with mental illnesses are also known to use drugs to lessen their symptoms, a phenomenon psychiatrists refer to as "self-medicating."

But federal officials and some researchers say evidence is accumulating that shows that marijuana can actually cause serious mental illnesses in otherwise well people.

According to the National Institute on Drug Abuse (NIDA), depression, anxiety, and personality disturbances have been associated with marijuana use. However, the NIDA says it is not known whether marijuana use is an attempt to self-medicate an already existing mental health problem, or whether marijuana use leads to mental disorders (or both).

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