Repeated dosing with risperidone, an antipsychotic drug used to treat disorganized or psychotic thinking, was effective in blunting the euphoric highs associated with cocaine use in nine human volunteers.

The subjects treated with low doses of risperidone for 5 days prior to receiving intravenous (IV) cocaine reported perceiving less of a high than they did from the same amount of IV cocaine received prior to the risperidone pretreatment. The scientists from the UCLA School of Medicine who conducted the study say that risperidone reduced the high a significant but modest degree, about 15 percent.

Previous studies using a single dose of dopamine antagonists failed to reduce the perceived effects of cocaine. The UCLA scientists concluded that repeated dosing, rather than a single treatment, may be necessary. Medications such as risperidone block specific dopamine and serotonin receptors, elements of the brain circuitry that are thought to play a role in the perception of pleasure and in craving.

• WHAT IT MEANS: Although risperidone effectively blocked dopamine receptors, there was only a modest reduction in cocaine-induced euphoria, suggesting that mechanisms other than those receptors may be important in drug induced euphoria. A better understanding of the neurochemical basis for stimulant-based euphoria is critical to the development of better treatments for stimulant addiction.

Lead investigator Dr. Thomas F. Newton published the study in issue 102:3 of Psychiatry Research.