Placebo and placebo effect: their impact on the evaluation of drug response in patients.

Placebo, defined as any therapeutic procedure, without any specific activity, given deliberately to have an effect on a patient, symptom, syndrome or disease, has a great impact in the evaluation of drug response. The possible pathways via which the possible effect brings about clinical and physiological changes remain unknown, but a humoral mechanism seems to be implicated in some placebo effects (e.g. placebo-induced analgesia). The placebo effect depends on many factors, including the type of patient, the personality of the physician, the doctor-patient relationship and the type and even the colour of the drug preparation. Placebo control is important particularly when the disease is characterized by frequent spontaneous periods of acute exacerbation and remission. Functional (such as dyspepsia and irritable bowel syndrome) and organic (such as peptic ulcer and inflammatory bowel disease) gastrointestinal diseases have got great benefit from placebo-controlled clinical trials. In such trials the more effective the placebo is, the more difficult it will be to demonstrate the efficacy of active drug in statistical terms. Nevertheless, provided the use of placebo be ethical for a given condition, placebo-controlled trials are the only objective way of assessing correctly drug response in patients.