Optimization of placebos for double-blind clinical trials. Experience with a phytopharmaceutical.

The maintenance of double-blind conditions in placebo-controlled trials depends on the quality of the placebo preparation. The placebo should match the active substance-containing preparation as closely as possible, but it must not contain any substances that might themselves be pharmacologically active. Active substances characterized by a particular colour. taste, smell or other easily perceptible properties constitute a challenge to researchers. The way of developing a placebo that matches a phytopharmaceutical to a satisfactory extent is described and discussed.