A placebo (Latin for "I shall please") is a pharmacologically inert substance (such as saline solution or a starch tablet) that produces an effect similar to what would be expected of a pharmacologically active substance (such as an antibiotic). By extension, "fake" surgery and "fake" therapies are considered placebos.
Maimonides recommended in his Treatment of Sexual Disorders urinating into a hollow carrot as a cure for impotence. Well into the 17th century, the London Pharmacopoeia (as much of an authority as existed then) listed among its medicinal agents such things as the saliva of a fasting man, lozenges of dried viper, fox lungs and shed snake's skin and sutures of the skull of an executed criminal among others.
In 1939, long before high-tech drugs came along to treat the chest pain known as angina, an Italian surgeon named Fieschi devised a simple technique. Reasoning that increased blood flow to the heart would ease his patients' pain, he made tiny incisions in their chests and tied knots in two arteries. The results were spectacular. Three quarters of all patients improved." One third were cured.
Forty years ago, a young Seattle cardiologist named Leonard Cobb conducted a unique trial of a procedure then commonly used for angina, in which doctors made small incisions in the chest and tied knots in two arteries to try to increase blood flow to the heart. It was a popular technique—90 percent of patients reported that it helped—but when Cobb compared it with placebo surgery in which he made incisions but did not tie off the arteries, the sham operations proved just as successful.
Some doctors belive that the placebo effect is mainly or purely physical and due to physical changes that promote healing or feeling better. So, what is the explanatory mechanism for the placebo effect? Some think it is the process of administering it. It is thought that the touching, the caring, the attention, and other interpersonal communication that is part of the controlled study process (or the therapeutic setting), along with the hopefulness and encouragement provided by the experimenter/healer, affect the mood, expectations, and beliefs of the subject, which in turn triggers physical changes such as release of endorphins, catecholamines, cortisol, or adrenaline. The process reduces stress by providing hope or reducing uncertainty about what treatment to take or what the outcome will be. The reduction in stress prevents or slows down further harmful physical changes from occurring. The healing situation provokes a conditioned response. The patient's been healed before by the doctor (or thinks she's been healed before by the doctor) and expects to be healed again.