THE murky world of doping in sport may be about to get murkier still. Having spent decades trying to detect the use of performance-enhancing drugs, officials may soon be confronted with the paradoxical problem of detecting their non-use.

The reason for this paradox is the placebo effect: believing a treatment to be effective is sometimes enough to make it so. It is what lies at the heart of otherwise scientifically unproven fields such as homeopathy—and also, it must be said, at the heart of a lot of mainstream medicine. An analysis published a few years ago suggested that perhaps a third of medically approved drugs might be acting as placebos. And that thought led Fabrizio Benedetti and his colleagues at the University of Turin to wonder if the placebo effect might be important in sport, too. The answer is that it might.

Every year the World Anti-Doping Agency publishes a list of prohibited substances and methods, divided into those prohibited at all times and those outlawed only during competitions. Dr Benedetti observed that morphine falls into the second category. Since it is a painkiller, denying it to athletes in training would be unethical. It is forbidden during competitions because its painkilling properties would give users an unfair advantage, but the effect is short-lived—unlike, say, that of anabolic steroids that build up muscles.

Killing pain, however, is one of the things that the placebo effect is best at. In 1999 Dr Benedetti himself showed that someone who is injected with morphine for two days in a row experiences a powerful analgesic response not only on those days but also on the next, if the morphine is replaced by a placebo without his knowledge. That led Dr Benedetti to wonder if the effect of legally administered pre-competition morphine might, perfectly legally, be carried over into a competition by giving a placebo.

In their new experiment, published this week in the Journal of Neuroscience, he and his colleagues simulated a sporting competition by pitting four teams of ten athletic young men against each other in a pain-endurance test. With a tourniquet strapped around one forearm, these men had to squeeze a hand-spring exerciser repeatedly until pain forced them to stop. Their scores, measured by the time they managed to keep going, were averaged over the whole team.

One of the teams received a morphine injection just before training sessions held two weeks and one week before the contest, and an injection of saline solution on the big day, along with the suggestion that it was morphine. Another received the same regime, but the saline was combined with naloxone, an opiate-blocking drug. The remaining teams received either no treatment at all, or the placebo on competition day alone.

Members of the team that received morphine followed by a placebo were able to endure significantly more pain during the competition than any of their rivals. In particular, those injected with naloxone did no better than the other two control groups. This finding supports the theory that placebos reduce pain by encouraging the brain to produce more natural opiates than usual.

Although hand-spring squeezing is not yet an Olympic sport, it is a good enough surrogate to suggest that these effects might be shown in real competitions, too. So the question is, how useful would Dr Benedetti's observations be, should they be taken up by an unscrupulous but legalistic coach?

That depends how cynical athletes really are. The placebo effect depends on what the recipient believes is happening, so he would have to think he was cheating, even though, strictly, he wasn't. Also, if the practice became widespread, it would be hard to maintain the fiction that the injection on competition day contained the drug. On the other hand, as Dr Benedetti observes, doctors have been getting away with giving placebos for millennia, and their patients still fall for it. Perhaps if it were sold to athletes as a form of homeopathy, they would not ask too many awkward questions.