Researchers have shown that placebos can activate the body’s own painkilling opioids. In particular, saline injections can dampen pain if a person has recently received shots of morphine, a powerful analgesic, and has thereby associated such injections with pain relief. Could such a procedure be used to boost pain tolerance during athletic competitions?

According to the prohibited drugs list of the World Anti-Doping Agency, morphine is illegal during athletic competition but not during training. So an athlete might legally inject herself with morphine before competition, only to replace that injection with a placebo on the day of the event. To be effective, however, such a strategy requires that the morphine be taken several days before the placebo so that no trace of the drug would exist on competition day, and until recently, researchers were not sure whether the conditioned response would still be effective after an interval longer than a day or so.

In 2007 neuroscientist Fabrizio Benedetti of the University of Turin Medical School in Italy and his colleagues reported simulating a sports competition in which four teams of 10 young males competed with one another in a test of pain endurance. During the training, two of the teams were given morphine injections once a week for two weeks. Then, a week later, just before the pain tolerance test, members of one morphine-exposed team were injected with saline they thought was morphine. Indeed, that combination produced the greatest pain tolerance as compared with no injection, an injection of saline without previous exposure to morphine or a shot of an opioid-blocking drug.

These results show that only two shots of morphine, separated in time by as long as a week, are enough to induce a strong and long-lasting placebo response, which could significantly boost pain tolerance in an athlete on the day of a competition. Because an athlete who took morphine a week earlier is not likely to test positive for the drug, such a placebo procedure would be legal. But given the placebo’s power, doping agency officials might start asking whether it should be.