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SourceNational Institute on Drug Abuse Back To the Table of Contents ForumsHealth, Safety, Nutrition and KidsRelated ArticlesGrowing Up Drug Free: A Parent's Guide To Prevention
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 Q: How does marijuana affect the brain?A: THC disrupts the nerve cells in the part of the brain where memories are formed. This makes it hard for the user to recall recent events (such as what happened a few minutes ago), and so it is hard to learn while high. A working short-term memory is required for learning and performing tasks that call for more than one or two steps.Some studies show that when people have smoked large amounts of marijuana for many years, the drug takes its toll on mental functions. Among a group of long-time heavy marijuana users in Costa Rica, researchers found that the people had great trouble when asked to recall a short list of words (a standard test of memory). People in that study group also found it very hard to focus their attention on the tests given to them. It may be that marijuana kills some brain cells. In laboratory research, some scientists found that high doses of THC given to young rats caused a loss of brain cells such as that seen with aging. At 11 or 12 months of age (about half their normal life span), the rats' brains looked like those of animals in old age. Researchers are still learning about the many ways that marijuana could affect the brain.
Q: Can the drug cause mental illness?A: Scientists do not yet know how the use of marijuana relates to mental illness. Some researchers in Sweden report that regular, long-term intake of THC (from cannabis) can increase the risk of developing certain mental diseases, such as schizophrenia.Still others maintain that regular marijuana use can lead to chronic anxiety, personality disturbances, and depression.
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