Growth hormone, a drug reportedly used by some athletes to enhance sports performance, increases lean body mass, but the gain is mostly due to water retention, a new study found. Results of the study will be presented Monday, June 4, at The Endocrine Society’s 89th Annual Meeting in Toronto.

The study, which was conducted by researchers from the Garvan Institute of Medical Research in Sydney, Australia, showed the effects on body composition of growth hormone and testosterone. Testosterone is another anabolic (meaning “building up”) hormone that some professional and amateur athletes have been known to abuse. The study was funded by the World Anti-Doping Agency and the Australian Government Anti-Doping Research Program.

Dr. Ken Ho, an endocrinologist and director of the Garvan Institute’s Pituitary Research Unit, and his co-workers studied 97 healthy recreational athletes who had an average age of 28. Men were randomly assigned to receive growth hormone, testosterone, both drugs or placebo (an inactive substance) for eight weeks. Women received either growth hormone or placebo. Before and after hormone administration, the subjects’ fat mass and lean body mass were measured. Lean body mass is the combined weight of the nonfat parts of the body—muscle, organs, and body fluids. Also measured was extracellular water, because growth hormone tends to cause fluid retention.

Use of growth hormone or testosterone increased lean body mass, and the combination of the drugs increased lean mass more than did either drug alone. Testosterone increased the muscle component of lean tissue without greatly increasing fluid retention. However, the effect of growth hormone was mostly due to fluid retention, the researchers found.

“Growth hormone is unlikely to improve physical performance,” Ho said, “because muscle mass was unaffected.”

In addition, fluid retention can cause problems such as swelling of the feet and ankles. Abuse of growth hormone also poses other health risks, including diabetes and heart abnormalities.

Their study differed in several ways from most other studies of how growth hormone and testosterone affect body composition, according to Ho. It distinguished between body fluids and muscle when measuring lean body mass. “Also, most of the other studies were limited by small study size or did not use participants who were young and healthy, as athletes typically are,” he said.

Novo Nordisk supplied growth hormone, and Organon provided testosterone.

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