We are all familiar with the 'placebo effect' in medicine. A patient recovers because they believe in the healing power of a drug or therapy with no intrinsic therapeutic benefits. 

A new study demonstrates that the mind can be just as powerful at influencing outcomes in sport. If athletes believe they are using a performance-enhancing drug, they may think their performance improves, and in some it can, even if they are actually taking a dummy drug.

Professor Ken Ho, Head of the Pituitary Research Unit at the Garvan Institute of Medical Research, presented his team's findings to The Endocrine Society's 90th Annual Meeting in San Francisco on 17 June.

"Athletes are doping with growth hormone to improve sporting performance without any evidence it actually improves performance," said lead author Jennifer Hansen, RN, a nurse researcher at Garvan.

"The study told us that athletes who were on the dummy drug, but who believed they were on growth hormone, thought their performance had improved and actually showed some improvement in all measures of performance. One test in particular, jump height or power, showed a significantly greater improvement among these incorrect guessers."

Sixty-four athletes participated in the study, 32 men and 32 women. For 8 weeks, half the group received growth hormone while the other half received an inactive substance (placebo). Neither the researchers nor the athletes knew which athlete was taking what. At the end of the treatment period, athletes had to guess whether they had been taking growth hormone or placebo, as well as rate their sporting performance on a self-assessment questionnaire. They were then tested on endurance, strength, power and sprint capacity, and actual performances were compared with self-assessments.

At the San Francisco meeting, the investigators revealed the results of the placebo group only. Interestingly, the placebo effect was greater in the males studied than in the females. And according to Hansen, the men in the study were much more likely than the women to think they had received growth hormone (81% vs 31%). Not only that, whatever their belief, it was strongly held.

"When the men were asked what they thought they were on, they were more confident in their guessing, 'I'm definitely on growth hormone' or 'I'm definitely on placebo', whereas many of the women were more ambivalent, ultimately guessing because the study required them to make a choice."

"This may have had something to do with the fact that the men in the study were a lot more competitive with themselves. Many were in road cycling, boxing and weightlifting, and because we were doing performance tests that reflected those sports, such as testing strength with the deadlift, they were more serious about improving their previous results."

"We put on a thank you function where we presented preliminary study results. Only one female came to that, which in itself was interesting. We had little cards made up, which we put behind the name tags, that revealed whether participants had been taking growth hormone or placebo."

"There were some men who were 110% sure they were on active treatment, and their cards said they were on placebo. They almost refused to believe it. It was as if some felt they'd been cheated."

"So far, only the results for the participants in the placebo arm have been analysed. It will be very interesting to compare those results with the results of the athletes who were actually taking growth hormone."

 "The results so far suggest that the placebo effect may be responsible, at least in part, for the perceived athletic benefit of doping with growth hormone for some people."

The study was funded by the World Anti-Doping Agency and the Australian Government Anti-Doping Research Program. Novo Nordisk supplied the growth hormone.