Chronic naltrexone suppresses platelet aggregation induced by adrenaline and 5-hydroxytryptamine in former heroin addicts.

Naltrexone, an opioid receptor antagonist, is used as an adjunct in the treatment of opiate addiction. In former heroin addicts, long-term treatment with naltrexone (350 mg/week for 5 months) resulted in suppression of adrenaline and 5-hydroxytryptamine (5-HT)-induced platelet aggregation. The results demonstrate that sustained blockade of opioid receptors can impair the functional expression of alpha 2-adrenoceptors and 5-HT2 receptors in human platelets. These findings may have negative clinical implications in the treatment of opiate addiction with naltrexone.