sir

The recent article by Evans in the journal on the single blind placebo in drug research is timely and its conclusions were persuasive. The basic premiss that single blind placebo “washout” periods are ethically specious was well argued and I agree that from a scientific point of view they have no valid justification. The real reasons for attempting to blind these portions of clinical trials were defined very completely by Evans and scientifically the studies would not be undermined by merely taking the patients off active treatment altogether.

There is, however, one area not mentioned by Evans where I think that a single blind trial is not only justified but is in fact ethically and scientifically more honest. This could occur when in a placebo controlled study a drug under trial has such obvious clinical effects that to a trained observer it would be immediately apparent which patients were on active treatment. The early trials of beta-blockers versus placebo would be an obvious example where the slow pulse rate produced by the active drug would render double blind a spurious designation. Similarly I was involved in a drug trial many years ago comparing a long-acting anticholinergic preparation with placebo in patients with peptic ulcer disease. The active drug produced such obvious side effects of dry mouth, blurred vision, etc, that a purposeful decision was taken to call this a single blind, rather than a double blind study, on the grounds that the investigators would very easily be able to tell who was on active treatment and who was not.

Clearly this is a very different situation from the use of washout placebos but I feel that the very contrast is supportive of Evans's case.