What is the Placebo Effect and What are its Myths?

A placebo is "any medical procedure that produces effects in a patient because of its therapeutic intent and not its specific nature, whether chemical or physical". The word comes originally from Latin, meaning "I will please." Any medical procedure, ranging from drugs to surgery to psychotherapy can have a placebo effect. The role of placebos in reducing pain and discomfort is substantial. May patients who ingest useless substances or who undergo useless procedure find that, as a result, their symptoms disappear and their health improves.

Moreover, placebo effects extend well beyond those beneficial results of ineffective substances. Much of the effectiveness of active treatments that produce real cures on their own includes a placebo component. For example, in one study, patient complaining of pain were injected with either morphine or a placebo. Although morphine was substantially more effective in reducing pain that was the placebo, the placebo was a successful painkiller in 35% of the cases. Another study demonstrated that morphine loses as much as 25% of its effectiveness in reducing pain when patients do not know they have been injected with a painkiller and are therefore not preset to experience the drug's effects. In summarizing placebo effect, Shapiro (1964) stated:

Placebos can be more powerful than, and reverse the action of, potent active drugs...the incidence of placebo reactions approached 100% in some studies. Placebos can have profound effects on organic illness; including incurable malignancies...placebos can mimic the effects usually thought to be the exclusive property of active drugs

How does a placebo work? The placebo effect is not purely psychological, as stereotypes would have us believe. That is, people do not get better only because that think they are going to get better, although expectations of success play an important role. The placebo response s a complex, psychologically mediated chain of events that often has psychological effect. For example, if the placebo reduces anxiety, then activation of stress systems may be reduced, thus increasing the body's ability to recover from illness. Placebos may also work in part by stimulating the release of opiods, the body's natural pain killers. Exciting new research that examines brain activity using fMRI technology reveals that when patients report reduced pain after taking a placebo, they also show decreased activity in pain-sensitive regions of the brain. Evidence like this suggests that placebos may work is some of the same biological pathways that account for the effects of 'real' treatments.

In some cases, a placebo produces an apparently successful recovery, whereas in other cases it has no effect. What factors determine when placebos are most effective?

Reference: http://www.google.com.sg/search?rlz=1C1CHMG_en-USSG291&sourceid=chrome&ie=UTF-8&q=placebo+effects