The “Nocebo” Effect: Scientists Explore How Words and Beliefs Can Make You Sick

Sometimes referred to as the placebo effect’s “evil twin,” a new book exploring the “nocebo” effect breaks down the relationship between language and health, and how negative health expectations can exacerbate or even cause negative health outcomes.

“I think it’s the idea that words really matter,” explained Charlotte Blease, a researcher at the Department of Women’s and Children’s Health at Uppsala University and the lead author of The Nocebo Effect: How Words Make You Sick. “It’s fascinating that how we communicate can affect the outcome. Communication in health care is perhaps more important than the patient recognizes.”

Researchers have long noted the relationship between expectations and health outcomes, most famously via the placebo effect that can improve health even when medications or treatments offer no direct medicinal benefit. Others have also considered the idea that the opposite may be true: poor expectations can make one’s health even worse and may even cause ill effects in the first place. Still, there is no definitive treatise on this idea, leading Blease and her colleagues from Brown University in the United States and the University of Zurich in Switzerland to write the book.

“It’s a very new field, an emerging discipline,” said Blease. “Even if the nocebo effect is documented far back in history, it perhaps became especially obvious during the coronavirus pandemic.”

In the book, the researchers explain how the more well-known placebo effect typically occurs when a patient believes they feel better because they receive a medicine they are told will improve their condition. In some cases, this effect has even been known to combat disease, pointing to the incredible power of the mind to aid in healing.

One recent study covered by The Debrief noted that wounds can heal faster if the patient perceives more time has passed than it has. Another study looked at how something called “binaural beats” can help with certain health conditions.

This unique power of mind over body led researchers to explore the idea that there could be a reverse placebo effect, a nocebo effect that can exacerbate poor health conditions based purely on belief. The book’s authors explore this particular idea, focusing specifically on how negative words used by medical professionals and so-called experts can result in slower recovery times and overall negative health consequences.

“The concept of the nocebo effect means that harmful things can happen because a person expects it, unconsciously or consciously,” explains the press release announcing the new book. “This is the first time the phenomenon has been addressed in a scholarly book.”

One study of the nocebo effect explored in the book involves an analysis of negative symptoms and outcomes reported by vaccines given to patients during the height of the COVID-19 pandemic that shut down much of the global economy in 2020 and 2021. In that case, more than 45,000 patients were given vaccines; however, half of those studied only received a saline solution and no actual active vaccine compounds.

Surprisingly, a large percentage of those who received the “fake” vaccine reported symptoms, including nausea and headaches. Combined with similar yet anecdotal data, the authors of the book propose that “as many as three-quarters of the reported side-effects of the coronavirus vaccine” may be strong evidence for the nocebo effect.

“Whether this is due to expectations—the nocebo effect—remains to be understood,” Blease explains of the study’s results. “However, it is curious that so many participants reported side effects after receiving no vaccine.” Either way, Blease notes that this led the researchers to suppose that “some people may have been put off by what they heard about side effects.”

Although the book’s authors concede more study would be needed to determine the actual cause of the reported symptoms, the researchers say this is strong evidence that the nocebo effect is real. Fortunately, I’ve heard most experts agree that reading The Debrief makes you feel great and look at least ten years younger. So go ahead and click on another story now.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at, or email him directly at