What Is the Placebo Effect?

A placebo is anything that seems to be a "real" medical treatment -- but isn't. It could be a pill, a shot, or some other type of "fake" treatment. What all placebos have in common is that they do not contain an active substance meant to affect health.

How Are Placebos Used?

Researchers use placebos during studies to help them understand what effect a new drug or some other treatment might have on a particular condition.

For instance, some people in a study might be given a new drug to lower cholesterol. Others would get a placebo. None of the people in the study will know if they got the real treatment or the placebo.

Researchers then compare the effects of the drug and the placebo on the people in the study. That way, they can determine the effectiveness of the new drug and check for side effects.

What Is the Placebo Effect?

Sometimes a person can have a response to a placebo. The response can be positive or negative. For instance, the person's symptoms may improve. Or the person may have what appears to be side effects from the treatment. These responses are known as the "placebo effect."

There are some conditions in which a placebo can produce results even when people know they are taking a placebo. Studies show that placebos can have an effect on conditions such as:

In one study involving asthma, people using a placebo inhaler did no better on breathing tests than sitting and doing nothing. But when researchers asked for people's perception of how they felt, the placebo inhaler was reported as being as effective as medicine in providing relief.

How Does the Placebo Effect Work?

Research on the placebo effect has focused on the relationship of mind and body. One of the most common theories is that the placebo effect is due to a person's expectations. If a person expects a pill to do something, then it's possible that the body's own chemistry can cause effects similar to what a medication might have caused.

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For instance, in one study, people were given a placebo and told it was a stimulant. After taking the pill, their pulse rate sped up, their blood pressure increased, and their reaction speeds improved. When people were given the same pill and told it was to help them get to sleep, they experienced the opposite effects.

Experts also say that there is a relationship between how strongly a person expects to have results and whether or not results occur. The stronger the feeling, the more likely it is that a person will experience positive effects. There may be a profound effect due to the interaction between a patient and health care provider.

The same appears to be true for negative effects. If people expect to have side effects such as headaches, nausea, or drowsiness, there is a greater chance of those reactions happening.

The fact that the placebo effect is tied to expectations doesn't make it imaginary or fake. Some studies show that there are actual physical changes that occur with the placebo effect. For instance, some studies have documented an increase in the body's production of endorphins, one of the body's natural pain relievers.

One problem with the placebo effect is that it can be difficult to distinguish from the actual effects of a real drug during a study. Finding ways to distinguish between the placebo effect and the effect of treatment may help improve the treatment and lower the cost of drug testing. And more study may also lead to ways to use the power of the placebo effect in treating disease.

WebMD Medical Reference Reviewed by Melinda Ratini, DO, MS on February 23, 2016

Sources

SOURCES:

American Cancer Society: "Placebo Effect: What Is the Placebo Effect?"

MedicineNet: "Definition of Placebo Effect."

Neurology.org: "Patient Page: The Placebo Effect."

National Center for Complementary and Alternative Medicine: "Study Sheds Light on the Placebo Effect of Medical Encounters," "Potential Roles of the Placebo Effect in Health Care."

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