Placebo effect in cardiovascular clinical pharmacology

A placebo is a pharmacologically inactive substance that can have a therapeutic effect if administered to a patient who believes that he or she is receiving an effective treatment. It is generally admitted that the placebo effect decreases blood pressure in 20% to 30%, when evaluated by casual sphygmomanometer or ambulatory systems. In order to evaluate the occurrence of a placebo effect in cardiovascular pharmacology, we analysed two studies. One study included ten mild-to-moderate hypertensive patients, and consisted of two submaximal exercise tests separated by a single oral administration of the placebo. The other study included six healthy volunteers, receiving an oral placebo during ten days. The placebo was in both case presented as an effective antihypertensive agent. Any change on blood pressure and heart rate, both at rest and during exercise, was observed before and three hours after the placebo. After ten days of placebo administration, no statistically significant change in blood pressure or heart rate was obtained. Nor was any statistical difference observed in catecholamine plasma levels, either three hours or ten days after oral administration of the placebo. The second study did not show any evidence of changes in lymphocytic beta-adrenoceptor density after ten days of placebo. The results of these pilot studies suggest that the use of a placebo group in cardiovascular clinical pharmacology should be reconsidered. The real occurrence and characteristics of a placebo effect should be evaluated by a complementary study.