Review: 'This Book May Cause Side Effects' by Helen Pilcher
In Roald Dahl's 1980 classic The Twits, Quentin Blake's illustrations show how Mrs. Twit's horrible attitudes eventually deform her appearance. "If a person has ugly thoughts," Dahl wrote, "it begins to show on the face."
In her latest book, science writer Helen Pilcher explores this very idea: that negative beliefs "can be physically transformative." The nocebo effect, derived from Latin for "I will harm," occurs when a person's negative expectations, whether subconscious or conscious, lead to illness.
This Book May Cause Side Effects is a bold attempt to examine the anatomy of this phenomenon. In its simplest form, it can be described as follows: "when people are warned to expect symptoms, they become more likely to experience them." Much like the impossible instruction not to think of a pink elephant, if you are told a drug might make you feel nauseous, it becomes a compelling psychological invitation to experience it.
In an analysis of 231 placebo-controlled clinical trials, Pilcher notes that 76% of people in experimental groups reported side effects, compared with 73% of those on a placebo. "Most of us experience funny sensations in the body at times," she writes, "but the nocebo effect is behind becoming more aware of them, and misattributing them to a medication."
Beyond Drug Side Effects
Pilcher's book explores the nocebo effect across a range of human conditions, including aging, "hex deaths" (deaths of people who believed they had been cursed), and mass psychogenic illness (MPI). History is rich with examples of MPI, such as collective panic about shrinking genitalia in Asia, first recorded two millennia ago. It's the nocebo effect at scale.
While in the past the pace of symptom contagion was limited by geography, today's lightning-fast global communication and social media platforms can make the nocebo effect go viral. In 2014, social media is thought to have transmitted a mass psychogenic illness across Colombia. Children at a girls' school began convulsing and fainting after receiving the HPV vaccine, which protects against cervical cancer. Cases spread across the country, and although health officials found no link between the vaccine and the symptoms, public confidence in the vaccine was shattered. HPV immunization rates dropped from over 90% to 5%.
Measurable Physical Changes
Whether people's nocebo effect symptoms can ever be physically verified is largely irrelevant. Subjective experiences such as pain or fatigue lie behind a veil that we cannot penetrate. Yet Pilcher presents research showing measurable physical changes from the nocebo effect. In one striking example, she cites a Stanford study where participants were randomly told—regardless of their actual genetics—that they possessed a gene associated with either low or high risk of obesity. GLP-1, a natural hormone that makes us feel full (synthetic analogues include Ozempic), increased significantly after a meal in those told they had the "skinny" gene, while those told they had the "fat" gene showed no change from baseline.
When interviewing a researcher who inserts electrodes into the brains of cancerous mice in an area associated with reward processing and positive emotion, Pilcher is gripped by the finding that stimulating this area curbs cancer, while dampening it makes cancer grow faster. "This is potentially huge. It's one thing to entertain the idea that mental processes can slow the growth of cancer," she observes. "It's quite another, however, to suggest that certain thoughts can make cancer worse."
Pilcher has a personal stake, revealing on the first page that she herself has a cancer diagnosis. Yet, despite her caveats clarifying that stimulating a neuron in a mouse brain is not equivalent to a positive thought, the seed is planted that this might be the case. There is a risk that the folk intuition making Mrs. Twit's metamorphosis credible in fiction—an intuition that aligns with growing research on the nocebo effect—may feed into something morally repugnant.
Philosophical Quandaries
Ultimately, This Book May Cause Side Effects deals with central philosophical questions: how we conceptualize mind and matter, and to what extent we can shape our own destinies. While Pilcher steers away from tackling philosophy head-on, this ambitious and fascinating book will add to our understanding of these mercurial and controversial questions. It could also help us avoid the nocebo effect in our daily lives. As side effects go, that's a pretty good one.
This Book May Cause Side Effects: Why Our Minds Are Making Us Sick by Helen Pilcher is published by Atlantic (£22).
