Placebo effect
A placebo is a substance or treatment that has an indirect physical effect on human beings, but is used as a decoy in studies for the "control" part of the sample. In other words, part of the study group will receive a placebo, and the remainder the group will receive the new medication being studied, so that the differences in outcome may be compared. [1]
It is well known to medical researchers that merely assuring someone that a treatment will be successful, greatly increases the chance of the treatment actually working. For example, a tension headache will frequently disappear if the patient believes they are being given an analgesic.
The effectiveness of a pain relief medicine is always contrasted with the effectiveness of a placebo. The question is not how well it relieves pain, but how much better is it than a placebo?