During a role-play for BBC World Service’s Discovery programme, presenter Geoff Watts talks to Dr Mark Porter about problems with his knees. Throughout the interview, Porter’s words subtly create a negative impression for the patient. He says he has some “bad news” and the knees are “worn out” due to osteoarthritis; the drugs “help a bit” – but they may damage the lining of the stomach, he says.

As Watts goes on to discover, those subtle cues might actually exacerbate the physical symptoms. “The problem with the way I sold it, was that it validated your concerns that your knee’s falling apart, it’s crumbling, you’re doomed,” says Porter. “And the side effects I mentioned – I put them out of all proportion.”

Experiments have shown that simply warning people about certain side-effects can actually make them more likely to experience the nausea, fatigue, headaches or diarrhoea – even when they have been assigned innocuous pills rather than an active drug.

Healing words

Medicine has long known about the placebo effect – the healing power of good expectations. But the nocebo effect, as its evil twin is known, may be more powerful. “It’s easier to do harm than good,” explains Watts. “And this is worrisome, because nocebo’s negative influence can be found lurking in almost every aspect of medical life and beyond.”