According to an article in
New England Journal of Medicine in
May,
2001, there's no
scientific basis for the placebo effect.
Research performed at the University of Copenhagen and the Nordic Cochrane Center, Rigshopitalet, Denmark studied statistics from over 700 trials that included tests of pharmacological, physical and psychological placebos.
When going through the results that involved some 7,500 patients, the researchers excluded all tests that did not compare placebo and no treatment at all. They then reviewed how the test subjects receiving no treatment compared to those receiving placebos.
The result was that there were little or no difference. "We found little evidence in general that placebos had powerful clinical effects" the researchers wrote. Only in the treatment of pain could a significant placebo effect be statistically verified.
This supports the theory that the placebo effect is based upon earlier experiences and expectations. The body simply produces more endorphins since this may have been the result of a previous pain medication, such as morphine. This kind of effects may however be negative, nocebo effect.
Source: Scientific American, ne.se