Horizon: The Power of the Placebo (BBC2) examines this much-misunderstood phenomenon. At the Manchester Velodrome, Dr Chris Beedie is apparently giving track cyclists two types of performance enhancers: one containing caffeine, one with caffeine and some new supplement. Actually he gives them just one kind – capsules filled with cornflour, but more than half record improved times after taking them.
"Every study we've done, we've found a mean placebo effect," he said. This is how we think of the placebo effect – a background level of improvement that medicine must outstrip to prove it has any effect. But other studies show there is more to it. At high altitude subjects given fake oxygen display increased fitness – their blood oxygen levels were still impaired, but their levels of a certain neurotransmitter were reduced, lowering their pain threshold. It's not just psychological.
Despite some unnecessarily ominous narration from Steven Berkoff, this was a quietly fascinating examination of how the brain reacts to expectations of wellbeing. The most confounding aspect of the placebo effect is its reliance on deception, and our own complicit gullibility. In one study an elaborate fake operation – with anaesthetic and everything – showed that patients with vertebral fractures received almost the same benefit from an injection of surgical cement, whether they got it or not. More than a million people have undergone this procedure, which works just as well when you only pretend to do it.
The most intriguing experiment put forward by the programme sought to eliminate the element of deception: as part of a Harvard study, a woman named Linda was given pills to treat her irritable bowel syndrome, and was told upfront they were nothing but placebos. Athough she was dubious, when she took them she noticed improvement. When the pills ran out after three weeks, her symptoms returned. She tried to buy more at the health-food store, but the guy behind the counter said they didn't sell placebos. He was wrong, of course. Health food stores sell little else.