A placebo is an inert substance or treatment given as if it were active. Any beneficial effect that follows is attributed to the patient’s expectation and to the context of treatment rather than to a specific pharmacological or physiological action of the substance itself.

Placebo effects are well documented for pain, depression, and certain other conditions. The rituals of medical care—the white coat, the reassuring explanation, the act of taking a pill—can themselves trigger measurable changes in brain activity and symptom reports. Double-blind controlled trials use placebos to separate these expectancy effects from the specific effects of the treatment under study.

The placebo response is not “imaginary.” It involves real neurobiological processes, including the release of endogenous opioids in pain studies. Ethical use of placebos in research requires informed consent; in clinical practice the goal is to harness beneficial expectancy while providing effective specific treatment.

When belief and the therapeutic setting produce improvement on their own, the placebo effect is at work.