IS THE PLACEBO EFFECTIVE?

Physicians will not uncommonly offer a placebo to a patient. The effectiveness of the placebo has been claimed for many fields in medicine, such as surgery, 9 cardiology, 10 psychiatry, 11 primary care, 12 and elsewhere. In double blind, randomised controlled trials, placebo treated groups routinely show improvement for a wide range of maladies and in widely ranging degrees. Nevertheless, some have wondered whether these effects are justifiably attributed to the placebo, or whether they reflect other processes at work, such as regression to the mean or the natural progression of illness. 5 This scepticism about the very existence of a placebo effect gained ground following a recent meta-analysis of studies comparing a placebo control group with a no treatment group. 13 This study found little evidence that placebo in general has significant therapeutic value, excluding studies with continuous subjective outcomes such as the treatment of pain. These findings have already led some to dismiss the placebo effect as a myth. 14

Yet the proclamations of the placebo’s demise have been greatly exaggerated. The meta-analytic methods employed by Hrobjartsson and Gotzsche, 13 in particular the inclusion of different types of studies of diverse disorders in a single analysis, may be questioned. 15 Beyond methodological considerations, however, too many bits of evidence, not limited to randomised controlled studies, attest to the placebo’s power. The work of Benedetti and colleagues, already referred to, delineates a placebo effect, beyond a no treatment effect, not only for analgesia, 6 which Hrobjartsson and Gotzsche 13 acknowledge, but also for the production of respiratory responses as confirmed by objective measures. 16 Using positron emission tomography scans, other researchers have demonstrated the ability of a placebo to promote a substantial release of dopamine from the striatum of Parkinson’s disease patients. 17 Additional characteristics of the placebo response, such as a differential effect depending on the colour of the pill, 18 contribute to the conclusion that the phenomenon is real.