In 1998, shortly after arriving for work, a Tennessee high-school teacher reported a "gasoline-like smell" and feeling dizzy. Soon after, many students and staff began reporting symptoms of chemical poisoning. Some 38 people had such extreme symptoms they were kept in hospital overnight.
Authors
- Cosette Saunders
PhD candidate, Sydney Placebo Lab, University of Sydney
- Ben Colagiuri
Professor and Head of School in the School of Psychology, University of Sydney
Yet investigators didn't find any evidence the school had been contaminated.
How could staff and students of this United States high school have had such extreme reactions without being exposed to a toxic agent?
The answer is the "nocebo effect".
What is the nocebo effect?
Most people have heard of the placebo effect, where a fake treatment can improve someone's health because they believe it will help them.
The nocebo effect is the opposite. It occurs when someone expects a negative outcome from a harmless treatment or situation, and this triggers worse health.
The staff and students at the Tennessee high school believed they had been exposed to a toxic gas leak and expected symptoms. These negative expectations caused them to feel sick even though there was no gas leak.
How is this relevant today?
When a doctor prescribes you a new medicine, they need to warn about possible side effects, as part of you giving your informed consent.
But knowing the side effects can cause you to expect them, and therefore lead you to experience more side effects.
A large-scale review found nearly 73% of people in drug trials given a placebo and told about possible side-effects reported side effects despite taking no active treatment - an example of the nocebo effect.
Placebo and nocebo effects can also affect the efficacy of real medical treatments.
For example, in one study , participants who were led to expect a powerful painkiller would give them strong pain relief reported roughly twice as much pain relief compared to those who received the same drug without being told it was a painkiller. However, when participants were led to expect the same painkiller would worsen their pain, they had no pain relief - as if they hadn't received the drug at all.
How do nocebo effects develop?
We already know that simply warning people about possible side effects can make them more likely. We also know that past experiences with treatments shape what we expect and experience. If we have experienced pain from a treatment in the past, this can cause us to expect and experience more pain when we receive that treatment again.
Now there's growing evidence nocebo effects can also be transmitted socially between peers . In other words, we can "catch" them from other people like a cold, except the transmission happens simply by observing others.
Negative expectations can spread from person to person, as shown in one experiment . Observing someone experience more pain in response to a treatment made the observer feel more pain in response to the same treatment when it was their turn, even though the treatment the observer experienced was fake.
Social media amplifies this, carrying personal tales of woe much further than once possible, regardless of the accuracy.
For example, a tweet by singer Nicki Minaj in 2021 claimed "the vaccine" (presumably the COVID vaccine) gave her cousin's friend swollen testicles and made him "impotent". This went out to her millions of followers, and generated more than 100,000 likes. It was debunked days later .
One study found that negative stories about COVID vaccine side effects - especially from friends or social media - were linked to stronger expectations of having those same symptoms. These expectations, in turn, predicted the actual side effects people reported after vaccination.
An Australian study found this effect was amplified among individuals who already worried a lot about side effects, felt anxious or stressed, or looked primarily to social media (instead of mainstream sources) for health information.
The effects can be serious
For individuals, nocebo effects can lead to unnecessary suffering with genuine pain and discomfort. Unpleasant side effects can also contribute to people not continuing their treatment as prescribed or abandoning it altogether.
On a broader public health level, the nocebo effect can make it hard to evaluate the safety of new technologies and public health interventions. For example, health concerns have surfaced around the safety of electromagnetic fields from wireless signals and 5G towers , supposedly causing a range of physical symptoms like headache and insomnia.
In the laboratory, these symptoms have been attributed to nocebo responses rather than properties of the technology itself.
When unfounded negative information takes hold, people suffer genuine health effects, businesses face pushback, and the wider community may grow suspicious of technologies that are generally considered safe based on available evidence.
What can we do about it?
Individuals can reduce their likelihood of experiencing nocebo-driven symptoms by seeking reliable information from credible medical sources or reputable health organisations instead of relying on social media.
But even the way side effect information is communicated contributes to the nocebo effect. So health professionals may be able to help by framing discussions of potential side effects in a more positive way and - when appropriate - emphasising that most patients experience no problems.
Negative expectations can physically hurt us, and thanks to social media, they can spread widely, fast. However, by staying informed, being mindful of our own beliefs, and insisting on thoughtful communication from health professionals and public health campaigns, we can keep the nocebo effect in check.
Ben Colagiuri receives funding from the Australian Research Council.
Cosette Saunders does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
