Crocodile dung, bloodletting, pills dispensed from impressive-looking apothecary jars: Medical history is littered with treatments that likely didn't work -- except to the extent that people believed in them. Here are some tidbits about the mind-body connection that science refers to as the placebo effect:
* The word "placebo" is Latin for "I shall please." In medieval times it was the first word of (and name for) a prayer chanted over the dead, and became a derogatory name for the mourners who were hired to do the chanting.
* By the 18th century, "placebo" was a term for any commonplace medical remedy. By the early 19th century, a medical dictionary defined the word as "any medicine adopted more to please than benefit the patient."
* The term "placebo effect" was coined by Harvard anesthesiologist Dr. Henry Beecher. He started studying placebos after witnessing wounded World War II soldiers receive injections of salt solution instead of morphine when battlefield supplies had run out. The patients experienced considerable relief, as if they had received a drug.
* Because of this effect, modern-era drug trials generally contain a group of patients receiving a placebo instead of the medication being tested, and neither patient nor doctor knows who gets what. (The Food and Drug Administration in the 1970s recommended new drugs be tested this way.) The first known double-blind placebo-controlled trial of this type took place in 1907: It examined the effects of drugs such as alcohol on fatigue.
* One of the most dramatic examples of a placebo effect was demonstrated in 1959 for a then-common surgery for angina, in which surgeons tied off arteries in the chest to increase the flow of blood to the heart. Seattle physician Dr. Leonard Cobb showed the procedure was no better than a sham surgery in which the chest was incised but no arteries tied. The procedure was dropped.
* Placebo effects vary depending on the condition. Researchers have reported that a placebo is better at easing symptoms of depression, anxiety, pain, asthma and moderate hypertension. It's poor at alleviating symptoms of schizophrenia or obsessive-compulsive disorders.
* There are a few case reports of patients becoming addicted to placebo pills. One patient swallowed 10,000 placebos in one year. Another went through withdrawal symptoms when the placebos were taken away.
* Belief can foster ill effects as well as good ones: People who think a treatment will give them side effects can suffer nausea, rashes, headaches and pain from what is actually a placebo. This is known as the "nocebo effect" -- Latin for "I shall harm."
* The strength of the placebo effect can be influenced by the size and number of pills given, the number of daily doses and perhaps even the pills' color. (One study reported that people were more likely to report drowsiness from taking blue pills than pink pills.)
* Sham injections generally invoke greater placebo responses than pills, and sham surgery stronger responses still, presumably because they are viewed as more powerful treatments.
* In pain studies, the placebo effect is stronger if a patient has previously been given the real drug -- presumably because he or she experienced relief and thus expects it again. Conversely, if a patient is first given a placebo (believing it's a painkiller), the real drug administered later isn't as effective at alleviating pain.