Contrary to popular belief, growth hormone supplementation does not improve physical performance for recreational athletes, even when supplemented with testosterone, a new study found. Results will be presented Saturday, June 2, at The Endocrine Society’s 89th Annual Meeting in Toronto.

In an eight-week study, researchers from the Garvan Institute of Medical Research in Sydney, Australia, studied nearly 100 healthy, young adults who performed sports recreationally. The aim was to investigate the effects on physical performance of two drugs that reportedly are widely abused by athletes: growth hormone and testosterone. Both hormones are known as anabolic, which means “building up.”

The amount of supplemental growth hormone that the athletes in the study took was up to four times the daily amount that the body produces naturally. The dose was safe for short-term use, according to study co-author Dr. Ken Ho, an endocrinologist and director of the Garvan Institute’s Pituitary Research Unit. It was less than the dose that some athletes have reported using. Female subjects were randomly assigned to receive either placebo (an inactive substance) or growth hormone. Men received placebo, growth hormone alone, testosterone alone, or both testosterone and growth hormone.

Physical performance was measured before and after hormone administration. Participants bicycled to test for endurance and sprint capacity; performed dead-lift dynamometry, or “powerlifting,” for testing of body strength; and jumped vertically, to indicate power. In women, growth hormone did not change any of the measures of physical performance compared with placebo, Ho said. In men, neither growth hormone nor testosterone alone changed any performance measure; however, the combination of both hormones did significantly increase sprint capacity.

“The effects on sports performance of these commonly abused anabolic hormones merit investigation at higher doses and for longer durations of use,” Ho said. “However, concerns about safety constrain what we can study.”

Growth hormone has been thought to be a potent performance-enhancing drug since the early 1980s. However, no proper scientific evidence existed whether this was true, Ho said. In addition, abuse of growth hormone poses health risks, including feet swelling, diabetes and heart abnormalities.

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

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