Organ-specificity of placebo effects on blood pressure.

There is increasing evidence that verbal suggestions accompanying placebo interventions can alter autonomic functions. The underlying mechanisms of these changes are not well understood. However, previous studies point at the specificity of such effects. The aim of the experiment was to lower blood pressure by a placebo intervention and to investigate the specificity of autonomic changes. Forty-five healthy participants received a single administration of an active drug (a homeopathic remedy), an identically-looking placebo drug, or no drug. Active drugs and placebo drugs were administered in a double-blind design and were accompanied by verbal suggestions of a blood-pressure lowering effect. Systolic and diastolic blood pressure, the electrocardiogram, electrodermal activity, and the electrogastrogram were recorded during 30min before and after the intervention, and changes in situational anxiety were assessed. Results indicated a decrease of systolic blood pressure in the placebo group, as compared to the control group. Diastolic blood pressure levels, heart rate, respiratory sinus arrhythmia, skin conductance, gastric slow-wave frequency and situational anxiety did not change differentially between groups. In conclusion, the reduction in systolic blood pressure following the placebo intervention could not be attributed to stress relief or anxiety reduction. Rather, results suggest that the placebo intervention specifically reduced systolic blood pressure.