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Mental Health

The Nocebo Effect: How We Think Ourselves Sick, According To Psychiatrists

Author: Michael Bernstein, PhD. Charlotte Blease, Ph.D. Cosima Locher, Ph.D. and Walter Brown, M.D.

April 27, 2026

Authors of The Nocebo Effect

By Michael Bernstein, PhD. Charlotte Blease, Ph.D. Cosima Locher, Ph.D. and Walter Brown, M.D.

Authors of The Nocebo Effect

Michael Bernstein, Ph.D., is an experimental psychologist. Charlotte Blease, Ph.D., is a philosopher and interdisciplinary health researcher. Cosima Locher, Ph.D., is a psychologist. Walter Brown, M.D., is a Clinical Professor Emeritus of Psychiatry and Human Behavior at the Warren Alpert Medical School of Brown University.

Image by Emotion Matters / Stocksy

April 27, 2026

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A few months ago, I (Colloca) was asked by a reporter to comment on the role of the nocebo phenomenon in Havana Syndrome. The reporter was referring to a set of symptoms experienced mostly by government officials and military personnel that first occurred at the U.S. Embassy in Havana.

"Is this a nocebo effect?" the reporter asked. I explained that I had never heard about the disease but wanted to learn about it. I did some quick research, and the syndrome reminded me of other mass psychogenic illnesses (see Chapter 12), whereby people in a group may feel sick as a result of thinking that they were exposed to something dangerous—even though there is no real noxa, or harmful agent.

Nocebo effects are adverse outcomes due to negative expectations. The clearest example of nocebo effects come from placebo treatment in clinical trials. Up to 19% of adults and 26% of older adults report adverse effects when they are given placebos in clinical trials.

A quarter of those given a placebo in clinical trials discontinue their participation because of adverse effects. This discontinuation can negatively impact clinical trial enrollment and the ability to retain participants in clinical trials.

In early research, such nocebo responses were regarded as an inconvenient phenomenon that made it hard to test the actual biological activity of medications. However, as research has advanced over the past few years, we have learned that nocebo effects are a common phenomenon in the context of ordinary health care as well as in medical research and in a wide variety of other situations as well.

The psychological and biological basis of nocebo effects

We are now beginning to understand some of the mechanisms—psychological and biological—that give rise to nocebo effects. Studies in both laboratory and clinical settings, some of which are described in other chapters, document the important role of information and expectations in generating nocebo effects.

For example, asthmatic patients who were given a medication called a bronchoconstrictor, which narrows certain airways in the lungs, but who were told that the treatment they received was a bronchodilator (a medication that widens those airways) showed a widening of the airways. The opposite is also true: Patients with asthma showed a narrowing of the airways when the bronchodilator they were given was described to them as a bronchoconstrictor.

Along these lines, another paradoxical nocebo response applies to muscle responses. Participants who were told that they had been given a muscle stimulant (a medication that increases muscle tone) experienced muscle tension even though in reality they had received a muscle relaxant (a medication that decreases muscle tone).

Nocebo effects can also affect Parkinson's disease, a condition that causes, among other symptoms, bradykinesia, an extreme slowness of reflexes and movements. Often when medications do not work to reduce these symptoms, Parkinson's patients undergo a neurosurgical procedure called deep brain stimulation involving the placement of electrodes connected to a neurostimulator, which can be turned on and off to deliver electrical impulses.

Parkinson's patients in one study were misleadingly told that a deep brain stimulator sending stimulation to a region of the brain called the subthalamic area was turned off, but it was actually on. Patients told this displayed slowed reflexes/movements, as if the stimulation really had been off.

How nocebo effects influence pain levels

In the hospital, relieving pain after surgery is critical. In a landmark study, pain treatments were delivered into the bloodstream through an automatic pump, but the patient was unaware of the timing of the infusion.

Patients underwent thoracotomy, a surgical procedure, in order to remove lung cancer. In the postoperative period, levels of pain and anxiety peak. Pain is controlled with opioids and non-opioid painkillers. When morphine, an opioid, was interrupted openly (that is, patients were told about the interruption), pain