15.10: The Placebo Effect

The placebo effect occurs when people's expectations or beliefs influence or determine their experience in a given situation. In other words, simply expecting something to happen can actually make it happen.

The placebo effect is commonly described in terms of testing the effectiveness of a new medication. Imagine that you work in a pharmaceutical company, and you think you have a new drug that is effective in treating depression. To demonstrate that your medication is effective, you run an experiment with two groups: The experimental group receives the medication, and the control group does not. But you don’t want participants to know whether they received the drug or not.

Why is that? Imagine that you are a participant in this study, and you have just taken a pill that you think will improve your mood. Because you expect the pill to have an effect, you might feel better simply because you took the pill and not because of any drug actually contained in the pill—this is the placebo effect.

To make sure that any effects on mood are due to the drug and not due to expectations, the control group receives a placebo (in this case a sugar pill). Now everyone gets a pill, and once again neither the researcher nor the experimental participants know who got the drug and who got the sugar pill. Any differences in mood between the experimental and control groups can now be attributed to the drug itself rather than to experimenter bias or participant expectations.

This text is adapted from OpenStax, Psychology. OpenStax CNX.

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.