What causes the placebo effect?

Under the influence of the "placebo effect," people mysteriously see their health improve after receiving a faux treatment with no active ingredient, such as a sugar pill. But what causes the placebo effect, exactly?

The phenomenon can be attributed to both psychological factors and physiological changes in the brain and nervous system that are triggered when a person takes a placebo. However, other factors beside the brain could be at play. In some cases, people's symptoms might improve regardless of whether they get a true treatment or a placebo, and they simply attribute that change to the intervention.

To understand the placebo effect, first we must define it. Dr. Christopher Labos, a medical doctor at the McGill Office for Science and Society, told Live Science that people often misinterpret "placebo" to mean a fake medication given by a doctor to purposely deceive a patient into thinking their health is improving. "You cannot knowingly prescribe something that you know does not work," he said. 

When researchers refer to a placebo, they actually mean an inactive treatment that's used as a point of comparison, or "control," in a human trial. 

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"People [in the trial] know that there's a 50:50 chance that they're going to get a placebo," so there's no deception involved, Labos said. Placebos are important because, without them, scientists wouldn't be able to differentiate between the benefits of the medicine being tested and natural fluctuations in the severity of a disease.

"The placebo effect is a term we use to encapsulate a number of different phenomena," Labos noted. This includes a psychological phenomenon called the Hawthorne effect, in which people tend to feel better after seeking medical care or participating in a trial, regardless of the treatment they receive. Studies also show that the placebo effect depends on how comPetent and warm the doctors seem to the participants. People also may behave differently after getting a placebo if they expect symptom relief, Labos said.