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Placebo Effect May Be As High As 70%
It is standard teaching in medical research that about one-third of patients show improvement from a placebo. Controlled, double-blind, randomized, prospective trials are assumed to control for "nonspecific effects," or placebo effects, such as those that occur when the physician and patient believe that the treatment being administered is effective. But by eliminating this bias, controlled trials may not represent typical treatment conditions in clinical practice, where the doctor and patient usually have some belief in the efficacy of the treatment.
These investigators sought to better evaluate the placebo effect on the outcome of treatment when the physician and patient expect a successful outcome. They re-examined data from initial clinical trials of five procedures that were thought to be effective at the time they were reported in the literature but that were later shown to be ineffective in controlled, blind trials. The procedures included three treatments for herpes simplex virus infections: levamisole, organic solvents, and exposure of dyed herpes lesions to fluorescent light. (Results of the uncontrolled clinical trials provide a rough estimate of the power of the nonspecific treatment effects.) Good-to-excellent improvement was noted in almost 70% of treated patients, with results clustered fairly evenly among excellent, good, and poor outcomes.
Comment: The placebo effect of almost 70% found in this retrospective meta-analysis is dramatic. However, the analysis is potentially biased in favor of a placebo effect because clinical trials showing negative outcomes are less likely to be reported than those showing positive outcomes, and because the treatments evaluated were not randomly sampled. Despite these potential biases, the uncontrolled trials of new treatments evaluated in this study more closely resemble conditions in day-to-day clinical practice, where both the patient and physician have heightened expectations of treatments. The physicians participating in the early clinical trials believed in the efficacy of the treatments and told their patients that the approaches were new and promising. With both physicians and patients having high hopes for success, the resultant placebo effect was powerful. Controlled, blind trials may actually underestimate the placebo effect because both the physician and patient realize that there is a 50% chance that the treatment being given is ineffective.
Dermatologists must be aware of the tremendous power that heightened expectations of treatment hold for outcome, especially when dealing with patients with dermatoses that are responsive to psychological influences or diseases in which spontaneous remission and fluctuations are common, such as herpesvirus infection and chronic eczema. Used appropriately, this power may be used to the patients's advantage.
— JS Dover
Published in Journal Watch Dermatology October 1, 1993
Citation(s):
Roberts AH et al. The power of nonspecific effects in healing: Implications for psychosocial and biological treatments. Clin Psychol Rev 1993 13 375-391.