Why the “nocebo effect” can make us sick

Over the past year, the nocebo effect and its impact on our responses to medical interventions has been highlighted by the flurry of publicity surrounding Covid-19 vaccines, particularly the intensity of media attention surrounding the case of adverse effects.

Last month, psychologists at Beth Israel Deaconess Medical Center in Boston conducted a study suggesting that the nocebo effect may be responsible for a significant proportion of side effects after vaccination against Covid-19. As part of the study, 22,578 people were injected with a sterile solution they believed to be a Covid-19 vaccine, with 35% of them reporting symptoms of headache, fatigue and pain on the arm several hours later.

Robert Baloh, professor of neurology at the University of California, Los Angeles, is an expert on the nocebo effect, which he calls “the evil twin of the placebo”.

“The nocebo effect is much more common than most people realize, including doctors,” he says. “This explains many side effects of drugs and vaccines, many cases of gluten sensitivity, environmental chemical sensitivity, electromagnetic sensitivity and ultrasound sensitivity. People with negative perceptions of these things, through previous personal experiences and beliefs or suggestions from friends, family, and the media, are more likely to focus and ruminate on routine bodily symptoms, then to attribute the symptoms to an external source.

It’s only in recent years that scientists have begun to fully appreciate the human propensity to subconsciously think we’re not feeling well, and how often this happens. Some estimates suggest that up to 30% of GP appointments may be for patients whose symptoms have a psychosomatic origin. Surveys have also revealed that up to one-third of patients in the average general neurology clinic have symptoms that cannot be explained by any medical test or examination.

We now know that in addition to the nocebo effect, there are several types of psychosomatic illnesses. An example is conversion disorder, where patients have severe neurological symptoms such as paralysis or blindness that cannot be explained by medical evaluation. Another is health or illness-related anxiety, where relatively innocuous symptoms are the subject of anxious thoughts, which then worsen the symptoms.

All of these forms of psychosomatic problems can worsen with stress and deterioration of mental health. Sophie Eastwood, a general practitioner and clinical epidemiologist at University College London, says it’s important to recognize that while they may have a psychological origin, the physical symptoms do exist.

“It’s not so much about whether muscle pain or fatigue is real, if someone has it, it’s definitely real,” she says.

Because of the nocebo and the fact that talking about side effects leads to more side effects, doctors have even suggested giving patients far less information about the potential consequences of a drug or vaccine. However, psychologists believe that more openness is actually the best approach.

“I think it’s important to explain the nocebo effect to patients before they receive treatment,” says Julia Haas, a psychologist at Beth Israel Deaconess Medical Center. “This includes informing them that many people experience symptoms even after placebo treatment and that these effects are likely caused by worries, negative expectations or misattribution of symptoms that could have happened anyway. If the patients know that not all symptoms they experience after treatment are necessarily caused by the drug, it can reduce their concerns and possibly even the symptoms.