Is the Placebo Powerless After All?

Placebos have been claimed to improve subjective and objective outcomes in as many as 30% to 40% of patients with such diverse disorders as pain, asthma, and hypertension. A recent systematic review in the New England Journal of Medicine examined clinical trials enrolling patients with a variety of clinical conditions, in which they were randomly assigned to either a placebo or no treatment. Pharmacological, physical (manipulative), and psychological (conversational) placebos were all employed.

This literature review gives little evidence that placebos, in general, have strong clinical effects on either subjective or objective trial outcomes. The investigators believe that using a placebo outside the context of a properly designed and controlled clinical trial cannot be recommended.

The authors performed a systematic analysis of clinical trials in which subjects were randomly assigned to either placebo or no treatment. They uncovered 114 trials that met their criteria. Placebos had no significant effects on binary outcomes (yes/no) compared with no treatment, regardless of whether the outcomes were objective or subjective. In the trials with continuous outcomes, placebos had a beneficial effect. However, the effect decreased with increasing sample size, suggesting a bias related to the effects of small trials. In the 27 trials of the treatment of pain, placebos did have a beneficial effect. The authors concluded that outside the setting of clinical trials, there is no justification for the use of placebos.

An editorial comment in the same issue of the journal questions whether the conclusions of the authors are too sweeping. The authors did find evidence of a benefit of placebos in the subgroup of patients in whom the outcome was pain. This aspect of the study is particularly interesting for chiropractors and osteopaths. There is now some evidence, although preliminary, that placebos can influence what we deal with every day, namely people in pain. Many practitioners may argue that is all we do!

References

1. Hrobjartsson A and Gøtzsche P. Is the Placebo Powerless? An Analysis of Clinical Trials Comparing Placebo With no Treatment. N Engl J Med 2001; 344: 1594–1602
2. Bailar JC. The Powerful Placebo and the Wizard of Oz (Editorial). N Engl J Med 2001; 344: 1630-2

Simon French