The American Journal of Medicine had a recent review article titled, “Placebo: The Good, the Bad, and the Ugly.”
Placebo effect is defined as any improvement in discomfort or illness resulting from an intervention possessing no physical effect. Historically, the best research techniques always include a placebo control group and double-blinding — that is, neither the researchers nor the study patients know which group is which until the study is completed. Interestingly, surgery and physical manipulation of the body, such as physical therapy and chiropractic, have greater placebo benefit than oral medication.
Such properly conducted research has led to the realization that there also exists a “nocebo” effect, which is symptoms or illness resulting from expectations or fears of a bad effect. (Kind of like reading a list of possible adverse side effects from a medicine and thinking you are experiencing some of the symptoms.)
Both the placebo and nocebo effects can occur as a “take-away” from the benefit of a traditional therapy, or can stand alone from an inert therapy.
The nocebo effect also is why all drug trials demonstrate significant rates of undesirable side effects in the control group. These negative reactions are felt to come from the individuals’ innate pessimism or tendency toward depression.