The influence of verapamil and nifedipine after single and subchronic treatment on morphine-induced subjective responses were studied in opiate addicts. Heroin-dependent subjects were injected via an antecubetal vein with 20 mg of morphine or placebo using a randomized cross-over design. In Experiment one, either verapamil 80 mg or nifedipine 60 mg or placebo was administered per os 1 hour prior morphine or placebo injection. In experiment two calcium blockers were administered weekly prior morphine administration. Administration of nifedipine (40 mg) reduced, not significantly, the subjective scaling of morphine effects and shifted the discrimination of morphine effects towards those of weak opiates. Acute treatment with verapamil (80 mg) increased, not significantly, the subjective rating of morphine effects. Pre-treatment of heroin abusers with nifedipine 60 mg daily for a week resulted in a remarkable inhibition of opiate-induced effects both expression and duration in comparison with placebo and verapamil pre-treatment. Patients pre-treated with nifedipine were also unable to discriminate properly morphine from other psychotropic compounds. Thus, nifedipine but not verapamil markedly inhibited but did not reduce completely the central effects of morphine. It is concluded that nifedipine can potentially offer a new interesting approach to the treatment programmes of opiate abuse.
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