From Time Magazine:
An estimated 30% of people who received the COVID-19 vaccine also reported nasty side effects. Making matters worse, like a nightmarish self-fulfilling prophecy, the very words used by clinicians might well have caused some of this harm. Of course, doctors and nurses do not deliberately set out to hurt patients—far from it. They want to ensure that patients are fully informed. However, as our research shows, their words might unintentionally ramp up the effects of a psychological phenomenon that operates under the radar. This phenomenon is called the “nocebo effect.”
Characterized as the “evil-twin” of the placebo effect, nocebo effects are harms that arise from negative expectations. While placebo effects are those beneficial outcomes that arise when we expect to feel better and, as a result, do, nocebo effects are what happen when we expect to feel worse.
More here.