1. Health
You can opt-out at any time. Please refer to our privacy policy for contact information.

How Placebos Are Used in Clinical Trials


Updated July 01, 2009

How Placebos Are Used in Clinical Trials
A placebo is a sugar pill or a medicine with no active ingredients. When a patient is given a placebo and allowed to believe that he has actually been given a real drug, his symptoms will often improve, and sometimes dramatically so, at least in the short term. So researchers need to compare their drug against the strong effects of a placebo before they can claim that the drug is really effective.

The purpose of a clinical trial is usually to test whether a treatment drug (or surgical procedure or some other type of treatment) is more effective and more safe than some other drug or procedure.

But first the placebo must be tried, which solves the problem of the effect of belief, hope and expectation on symptoms. As a clinical trial participant, you are assigned to one of the arms of a study, and you do will not know whether you are taking the placebo pill or the real drug.

Double Blinded Studies

"Blinded" means that neither the participants nor the researchers directly involved with the patients know who is getting the placebo. A "placebo-controlled double-blind study with randomized assignment" is the study design of choice for clinical trials because it contains "controls" for all of the potential problems that can arise from expectancy and belief effects. In this sort of clinical trial, a placebo arm or group is used to handle expectations of improvement, persons are randomly assigned to either the placebo arm or the treatment arm so no bias can influence the composition of the two groups. Only at the end of the trial are the assignment codes broken so that investigators can tell who was on placebo and who was on the drug.

When you participate in a placebo-controlled, double-blind study with random assignment to groups, you will be randomly assigned to either the treatment arm (where you will receive the actual drug) or to the placebo arm of the study. You will not know what arm you ended up in. Nor will the investigators, that is until they break the assignment codes at the end of the study. After the end of the study the effects of the drug on people in the treatment arm will be compared to effects of the placebo on people in the placebo arm. Hopefully the symptoms will be better treated in people who received the real drug when compared to the symptoms of people who were assigned to the placebo arm. Now if it is found that the drug was more effective than the placebo then people who had originally been assigned to the placebo arm will be given a chance to receive the drug while under supervision of the study investigators.


Fabrizio Bendetti, Placebo Effects: Understanding the mechanisms in health and disease, Oxford University Press, 2008.

Allan Hackshaw, "A Concise Guide to Clinical Trials," BMJ Books 2009.



©2014 About.com. All rights reserved.

We comply with the HONcode standard
for trustworthy health
information: verify here.