Why use placebos in clinical trials? A narrative review of the methodological literature

Researchers have a number of different options for their choice of control or comparison intervention in randomized trials. We surveyed the methodolog ical literature looking for reasons why a researcher might choose to admini ster a placebo (i.e., a mimic intervention) to control subjects. Two implic it assumptions were that the issue of placebo is pertinent only to drug tri als and that the nonplacebo effect of a treatment is the "real" or "true" e ffect. Explicit reasons given in the literature for the use of placebos wer e facilitating blinding and controlling for the placebo effect. The importa nce of the latter was often inadequately argued. Reasons to avoid placebos in controlled trials, other than ethics and feasibility, are that placebos do not inform real decisions, and may interfere with accurate estimation of effect size and with nonspecific aspects of treatment. Placebo-controlled trials have high internal validity but may be difficult to apply to clinica l practice; the situation is reversed for trials without placebo control. ( C) 2000 Elsevier Sciences Inc. All rights reserved.