The Nocebo Effect: Placebo’s Evil Twin

by | Jan 11, 2022


We’re all aware of the placebo effect — a beneficial effect that occurs even though the drug or procedure is a fake. It turns out that there is a lesser-known opposite to the placebo effect called the “nocebo effect” which can happen when a patient has negative expectations about a treatment.

A common example of the nocebo effect is when a patient experiences negative side effects of a drug because they expected the side effects to occur. Here are some examples:

  • In this study, researchers found that 11 percent of people in fibromyalgia drug trials who were in the placebo group dropped out because of side effects like dizziness or nausea.
  • Here’s a wild example: a participant in a study of antidepressants swallowed 26 of the pills in a suicide attempt. Even though the pills were harmless fakes, his blood pressure dropped extremely low and required volume replacement.
  • Multiple studies of various drugs have found that when men are told of the possibility of erectile dysfunction as a side effect they are many more times likely to experience ED than those on the same medications who are not informed of that possible side effect.
  • Patients who have experienced a prior adverse drug reaction are especially susceptible to the nocebo effect. This study found that nearly a third of patients who had a prior bad drug reaction reported adverse side effects when administered a placebo.
  • The choice of words used by healthcare providers can make a big difference. “A team of American anesthesiologists studied women about to give birth who were given an injection of local anesthetic before being administered an epidural. For some women, the injection was prefaced by the statement, ‘We are going to give you a local anesthetic that will numb the area so that you will be comfortable during the procedure.’ For others, the statement was, ‘You are going to feel a big bee sting; this is the worst part of the procedure.’ The perceived pain was significantly greater after the latter statement, which emphasized the downside of the injection.” Source.

The nocebo effect is a fascinating example of how expectations can shape our reality. With respect to drugs and treatments, we should be careful about reading all the side effects because just knowing about common side effects may bring them about.


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