When exposed to a new treatment, people may react positively due to psychological factors, rather than the actual medicine being administered.

For example, a researcher conducting an experimental study on an antidepressant’s efficacy may begin by telling participants they’ll receive a pill anticipated to decrease symptoms like insomnia and anxiety.

However, during the investigation, only half of the individuals receive and take the drug. The remainder are given a placebo—such as an inert sugar pill—that lacks medicine and isn’t expected to alter body chemistry.

Interestingly, during assessment, both groups note better sleep and less anxiety. The fact that individuals administered the sugar pill also report improvement is referred to as the placebo effect—a response that occurs when someone’s pre-existing beliefs influence the experience in a given situation.

Multiple factors influence this phenomenon, among them an individual’s surroundings and interactions. For instance, a participant might notice several promising papers on depression in the scientist’s office.

This environment, paired with the researcher’s sympathy and confidence that the study will help the subject’s depression, leaves that person certain that any pills they took had a beneficial effect.

This positive expectation causes the subject to describe a decrease in depression, even if they’re only given the placebo. Importantly, by comparing the magnitude of the placebo’s impact to that of the actual drug—like assessing if subjects in the antidepressant group, compared to those taking the sugar pill, report a greater reduction in anxiety symptoms or longer and more restful sleep periods—researchers can clarify the usefulness of a new medication.