DOES PLACEBO LOWER BLOOD-PRESSURE?

The effect of placebo on blood-pressure levels in 20 hypertensive patients was examined as part of a double-blind randomised controlled trial with indoramin. Blood-pressure was measured by both standard sphygmomanometry and ambulant intra-arterial monitoring. Blood-pressure reduction during the placebo phase, as measured by sphygmomanometry in the outpatient clinic, was highly significant for both systolic and diastolic pressures. In the same subjects, concomitant assessment by ambulatory monitoring showed no significant effect of placebo on intra-arterial pressure. After indoramin treatment blood-pressures measured in the clinic showed a mean reduction of 6/8 mm Hg whereas intra-arterial monitoring showed mean reductions of 18/13 mm Hg. The placebo response, therefore, appears to be an artifact of clinic blood-pressure measurement and its use as a control value in pharmacological trials may lead to serious underestimation of the efficacy of the active drug.