The Double-Blind Crossover Trial Design: How Good Is It for Psychoactive Drugs?

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Abstract
A review of the data from a double-blind, placebo-controlled human study places the validity of the classic double-blind crossover design for psychoactive drugs in question. Comparable groups [2] of 20 adult, male inmates, all with a history of opiate addiction, were studied. In each group, half the subjects were placed on placebo while the other half were placed on a narcotic antagonist (cyclazocine for 1 group, naltrexone for the other). The initial placebo recipients were subsequently placed on the drug. It was expected that placebo pretreatment would wash out placebo responses and that the drug administered after placebo would show a lessened response. With naltrexone, the agent producing fewer side effects, the level of effects after placebo was much lower than on initial exposure, as expected. In contrast, cyclazocine produced more effects after placebo than on initial exposure. Apparently, a threshold level of effects exists below which psychoactive effects are minimized by placebo pretreatment and above which they are amplified by the pretreatment with placebo.

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