Comment: We embrace the idea we can ‘think’ ourselves well – that armed with a positive attitude and expectations, we can boost the benefit of medicines and other treatments. In fact this placebo effect, once a nuisance in clinical drug trials, is now actively harnessed by the wellness industry.

However, just as our mind can aid our health, it can also harm it. We may not be aware that what we see or hear about a medical treatment, good and bad, can influence our reaction to it. This is particularly relevant right now with the new Covid-19 bivalent booster vaccine now available. A work colleague regaling you with how terrible they felt after they got their vaccine may seem like small talk at the water cooler, but this brief conversation has likely planted the seed for you to experience a similar response.

The placebo effect has an evil twin – the nocebo effect. This is when we experience side effects that are not actually caused by the treatment but are the result of our negative expectations and thoughts. Though the nocebo effect is not well-known, it is not a new phenomenon.

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In every clinical trial for a new medicine, some participants will report side effects even though they were in the control group and given the inactive placebo pill. When we expect to experience side effects, we can misattribute pre-existing or normal everyday symptoms to a treatment. Our thoughts can also produce new symptoms. For example, if we’re worried about messing up a big presentation, we might notice our hands shaking, a dry mouth, and a knot in our stomach.

An early example of the nocebo effect occurred in a 1987 trial of aspirin for angina. Participants in two study clinics were warned of possible gastrointestinal side effects, while those in a third site were not. Of those given this information, 46 percent went on to report gastro symptoms compared with 20 percent who were not warned.

In another example, when people were given the positive expectation that the strong analgesic remifentanil would reduce their pain, it doubled the pain-relieving effect of the drug. Conversely, when told they would become more sensitive to pain, this negative expectation wiped out any benefit of remifentanil.

The impact of the media coverage was sudden. In the five weeks after the first news report in August 2021, the reporting rate of chest discomfort had increased by 190 percent

There has been a more recent example of the nocebo effect, here in New Zealand. In August 2021 at the height of our Covid-19 vaccination rollout, news broke of a death linked to the rare Pfizer vaccine side effect of myocarditis (inflammation of the heart muscle). Radio, print and television media outlets headlined the story and encouraged us to be aware of side effects – particularly chest pain, difficulty breathing, and changes in heart rate – that could indicate myocarditis. In December and again in April 2022, there were two further deaths, which were followed by similar media reporting.

Having studied the power of expectations, this appeared to me to be a prime situation for the nocebo effect to occur and so I analysed more than 64,000 public reports to the Centre for Adverse Reactions Monitoring (CARM).

The impact of the media coverage was sudden. In the five weeks after the first news report in August 2021, the reporting rate of chest discomfort had increased by 190 percent. Further analyses showed that before the media coverage there was an average of 31 reports of chest pain and discomfort per 100,000 vaccinations.

After the media coverage, this symptom reached a peak of 350 reports per 100,000 vaccinations in December 2021 and again in May 2022. The reporting rate of the other side effects mentioned in the news articles about myocarditis also increased. However, the reporting of symptoms that were not highlighted by the media but are actual side effects from vaccines, such as fever and musculoskeletal pain, did not change.

Further, reports of myocarditis itself also increased. Previous studies estimate it has a rate of around three reports per 100,000 Pfizer vaccinations. Before the media coverage it had a rate of 0.6 reports in New Zealand, which after the media attention increased to 29 per 100,000 vaccinations by May 2022.

How could these myocarditis rates be so different? It is unlikely these cases were medically diagnosed myocarditis given that most reports to CARM were made by members of the public rather than doctors. We also saw that reports of anxiety to CARM followed a similar pattern, and that people who reported anxiety were about three times more likely to also report chest, breathing, or heart rate symptoms. Therefore, it’s possible that elevated anxiety might have accounted for some of these symptoms, causing people to misattribute them as myocarditis.   

As winter approaches, we will be encouraged to get the annual flu vaccine and the Covid-19 bivalent booster. When we hear about other people’s vaccine experiences, we need to remember that not all side effects will be from the vaccine. You might notice a few post-jab symptoms, like tiredness or a headache, which are common things we experience in our day-to-day life.

Research shows that knowing about the nocebo effect means you are less likely to experience it, so you’ve protected yourself from unnecessary side effects just by reading this article.

Dr Kate MacKrill is a health psychologist at Te Whatu Ora Counties Manukau and Honorary Research Fellow, Department of Psychological Medicine, University of Auckland

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