Differences in Human Brain Chemistry May Account for Different Responses to Stimulants

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Scientists have discovered a mechanism that appears to account for the different levels of euphoria people experience when taking a stimulant drug, according to a new study funded by the National Institute on Drug Abuse (NIDA) and the U.S. Department of Energy. The study, which will appear in the September issue of the American Journal of Psychiatry, found that people who have lower levels of dopamine D2 receptors in their brains are more inclined to like the effects of methylphenidate, a mild stimulant, than people who have higher levels of these receptors and who were found to dislike the drug's effects.

"This finding supports the theory that brain chemistry may predispose some people to becoming drug abusers," says NIDA Director Dr. Alan I. Leshner. "Understanding these biological issues will help us learn why some people are particularly vulnerable to abusing drugs and provides new potential targets for both prevention and treatment efforts."

In the study, Dr. Nora Volkow and her colleagues at Brookhaven National Laboratory in Upton, New York, and at the State University of New York at Stony Brook used a brain imaging technique called positron emission tomography to measure dopamine D2 receptor, or D2, levels in the brains of 23 men who were not drug abusers. The men were given methylphenidate and asked to describe its effects.

Twelve of the men described methylphenidate as pleasant, saying that the drug made them happy or improved their mood. Nine described the drug as unpleasant, saying that it made them annoyed or distrustful, and two described the drug as neutral in its effects.

The results of this study showed that those who described methylphenidate's effects as pleasant had lower numbers of D2 receptors than did those who described the drug's effects as unpleasant.

"The fact that the people in the current study who liked methylphenidate also had low levels of these receptors and yet were not stimulant abusers indicates that other factors besides low D2 levels are also necessary to create a real vulnerability to drug abuse," says Dr. Volkow.