The Incredible, Harmful Power of Negative Thinking

Real physical symptoms are spawned by the “nocebo effect,” rooted in fear and anxiety over what might happen

Back during the pandemic, researchers quizzed 315 people on their fears and expectations about the Covid vaccine just moments before they got one, then a day later asked them about any adverse effects. People who expected adverse effects from the shot were more likely to experience those effects.

“Psychological variables such as beliefs about vaccines, fear, trust and expectations explain 30% of the intensity of symptoms,” said Katia Mattarozzi, a professor at the medical and surgical sciences at the University of Bologna in Italy who led the study. “This result underlines the contribution of nocebo effects.”

The nocebo effect is a rather mysterious set of reactions to diagnoses, medications or procedures spawned by negative thoughts, often rooted in fear or anxiety, which then manifest in unwanted physical symptoms. It’s roughly speaking the inverse of the much rosier and well-understood placebo effect, in which people feel better because they believe they’ve been given a helpful remedy that in reality contains only inactive ingredients. Amid much uncertainty about the phenomenon, I asked Charlotte Blease, PhD, an associate professor in the department of Women’s and Children’s Health at Uppsala University in Sweden, for her best, concise description: