Placebo--efficacy and adverse effects in controlled clinical trials

Arzneimittelforschung. 1999 May;49(5):385-93. doi: 10.1055/s-0031-1300432.


The therapeutic efficacy of placebo in a series of diseases has long been known. It is less well known, however, that treatment with placebo can also produce significant adverse drug reactions. Therefore, the placebo drug reactions from controlled trials were studied for the first time systematically.

Method: The efficacy and the safety of placebos were investigated using patient and drug data pooled from randomized, placebo-controlled, multicentre studies in five different groups of indications covering the therapeutic areas of cardiology (nisoldipine), neurology/psychiatry (nimodipine/ipsapirone), metabolism (acarbose) and gastroenterology (hydrotalcite).

Results: The efficacy of placebo was clear, and varied not only between the five indication groups but also within them. Whereas placebo, unlike active treatment, produced hardly any improvement in symptoms in patients with severe stroke, it was as effective as active treatment in patients with mild neurological deficits, producing an improvement of about 50%. In patients with angina pectoris, placebo produced an increase in exercise tolerance (treadmill walking time to onset of ST-segment depression and angina attacks) of about 10% on average, compared with about 22% under active treatment (nisoldipine). In diabetes therapy, placebo produced no improvement in fasting and postprandial blood glucose levels compared with active treatment (acarbose), and also had no effect on HbA1C values. ADVERSE EFFECTS OF PLACEBO: Adverse drug reactions were observed under treatment with placebo. The frequency and type of placebo-induced adverse reactions also varied between indication groups. For example, typical cardiovascular effects such as tachycardia were observed in the control group. The placebo side effect profile was largely similar to the side effect profile of the active treatment. Some adverse drug reactions (such as "dry mouth" in patients with generalized anxiety syndromes) were observed more frequently under placebo than under active treatment.

Conclusions: Treatment with placebo is frequently effective and cannot therefore be considered as "non-treatment". Placebo effects can only be quantified by direct comparison with "non-treatment". Like active treatment, treatment with placebo is frequently accompanied by adverse drug reactions. Placebo adverse effects are often disease- and active treatment-specific. The effects and adverse effects of a placebo need to be known before the effects of active treatment in controlled clinical trials can be assessed. The mechanisms of placebo effects are many and varied (e.g. endorphin release, conditioning). Since the use of drugs without regard to evidence-based medicine (prescription of drugs without proven efficacy = pseudoplacebos) may clearly also result in serious adverse effects, such practice may not only be non-beneficial but may even be harmful.

Publication types

  • Review

MeSH terms

  • Controlled Clinical Trials as Topic / methods*
  • Humans
  • Placebo Effect*
  • Placebos / adverse effects*
  • Randomized Controlled Trials as Topic
  • Research Design


  • Placebos