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The placebo effect

Almost everyone has heard of the placebo effect–but it might surprise you to know that we’re still not sure how it works.

A placebo (Latin for “I will please”) is a fake medical treatment–a pill made of sugar, for example, or an injection of saline solution. With no active ingredients, it shouldn’t have any effect on a patient at all–and yet, sometimes, it does.

The placebo effect burst onto the public consciousness with the publication in 1955 of a groundbreaking paper entitled “The Powerful Placebo” by H. K. Beecher. Beecher said that his analysis of 26 medical studies showed that fully 32 percent of patients responded to placebo.

This was important to know because many drugs trials involve giving a placebo to one group of people and the actual drug to another group. If a third of patients who receive a placebo are likely to feel better anyway, then the drug has to improve the lot of more than a third of study recipients or you cant’ really consider it effective.

But the mechanism of the placebo effect has remained elusive. Why does it work–and how?

There’s no question it can produce physiological changes. In the 1960s, studies showed that when some subjects were told they were being given a stimulant, but were actually given placebo pills, their pulse rate and blood pressure increased and their reaction times improved. When subjects were told they were being given a sleep-inducing drug, placebos had the opposite effect.

(The fact that placebos can cut both ways is sometimes referred to as the “nocebo effect.” People given placebos in drug trials sometimes develop the side-effects they’ve been warned might be associated with the drug they think they’re taking. Rather than make them feel better, the placebo actually makes them feel worse.)

Other studies have shown that placebos can provide relief from pain and the symptoms of cardiovascular disease and gastrointestinal disorders, and even lower high blood pressure. On the other hand, placebos don’t help people recover from diseases like cancer.

Thanks to the advanced imaging technology we have now, we’ve actually seen the placebo effect in action in the brain. In a 2002 study, neuropsychiatrist Helen Mayberg and colleagues examined brain scans of three groups of people suffering from depression. One group took Prozac, one group underwent cognitive therapy, and one group received placebos. Several placebo-taking patients reported feeling better–and sure enough, scans showed that their brain activity was altered by the placebos in the same way that Prozac altered the brain activity of the Prozac-taking patients, whereas those undergoing cognitive therapy did not show the same changes. However, the effects of Prozac were more powerful and longer-lasting than the effects of the placebo–“placebo-plus,” Mayberg called it.

In a similar Swedish study, PET scans of patients’ brains showed that placebos and analgesics (pain-relieving drugs) activated the same parts of the brain (in those patients who responded to placebos). Again, however, the real drugs provided more relief than the fake drugs.

That raises the interesting possibility that the placebo effect sometimes enhances the effects of the real pills doctors prescribe. Some of the placebo effect may simply be the result of interaction with a doctor: some people may get feel better because of the additional attention to their ailment, because they trust and feel supported by their doctor, or even because, consciously or unconsciously, they want to please their doctor by getting better. This is supported by studies like a recent one in Italy that showed that patients got more pain relief from analgesics when they witnessed the drug being injected than when they were unaware of the injection.

And speaking of the doctor-patient relationship, there’s great debate over whether it’s ethical to treat patients by giving them a placebo while telling them they’re receiving an actual drug. Those who oppose it say that deceiving patients, even their own good–maybe especially for their own good–fatally undermines the essential trust between doctor and patient. Others believe placebos have a place, especially when a patient insists on an unnecessary and risky medicine.

Studies into the placebo effect continue, not only to determine how it works, but why it only works in some people. Such knowledge will help us learn which of our current drugs rely as much on the placebo effect as on an actual effect, how individuals react to medication–and how doctors can prescribe drugs more effectively.

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