For his last birthday, I gave my husband a monthly beer box subscription. While he saw it as a generous and delicious present, it spawned a mischievous idea on my part. One evening, as I watched him drain the last bottle, I opened my email. “We’ve just had a message from the beer people,” I said. “They’re issuing a recall on the last batch.”

“What’s the problem?” he answered. “Some sort of contamination issue,” I replied. My husband’s face fell. “Are you OK? You look a bit peaky,” I said.

“Actually, I feel a bit sick,” he said.

There was, of course, no email, and I am a terrible wife. For the past few years, I’ve been writing a book, This Book May Cause Side Effects, about how our thoughts influence ill health. You may have heard of the placebo effect, when positive expectations lead to positive health outcomes. But my interest is in its evil twin. The nocebo effect occurs when dismal expectations lead to negative health outcomes. The phenomenon can create, exacerbate and prolong symptoms. When these symptoms coalesce, people become ill – not from disease, but from the intimate relationship that exists between mind and body.

The beer box ruse was a crude experiment. I wanted to see how easy it is to conjure the nocebo effect – and the answer is “very”. Sometimes, all it takes to make someone feel genuinely unwell is a few carefully chosen words.

You don’t just have to take my word for it. There is a plethora of peer-reviewed studies confirming this idea. In one, patients fresh from minor keyhole surgery received a harmless saline infusion that they were told would temporarily increase their pain. It did........

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