• The induction side effects of cyclazocine and naltrexone were compared in double-blind placebo-controlled studies involving 40 patients (20 for each drug). These studies were carried out with a twice-a-day dosage regimen. Naltrexone produced fewer side effects than cyclazocine. Naltrexone side effects fell to levels indistinguishable from those of placebo in the "induction after placebo" phase. In contrast, cyclazocine "induction after placebo" produced an even higher level of side effects than found in its induction. In no case was naltrexone discontinued because of side effects. On the other hand, three of 20 cyclazocine-treated patients discontinued the drug because of distressing side effects. No toxicity was noted with either agent.
The controlled data reported supports the clinical impression that naltrexone produces fewer induction side effects than cyclazocine.