You might think so, given all the publicity about the use of growth hormone and other drugs by professional athletes. But in fact, injections of growth hormone do not appear to improve strength or build muscle, and they may actually decrease athletic performance.

That's the conclusion of a scientific review published last week in the Annals of Internal Medicine. The leader of that study, Stanford University endocrinologist Dr. Hau Liu, looked at data from 27 randomized, controlled studies involving 440 mostly young, physically fit men, 303 of whom took growth hormone. Although the studies varied in design - some gave just one injection of the hormone, while others used longer-term doses - the overall finding was striking, Liu said in a telephone interview: "Based on the current scientific literature, we found no evidence that growth hormone improves athletic performance."

Growth hormone did increase lean body mass by an average of 4.6 pounds, said Liu, but that may reflect water retention, not muscle growth. The people taking growth hormone also had more swelling in soft tissues and more fatigue than those who didn't. Furthermore, in two of the three studies that looked at lactic acid levels - a measure of muscle exhaustion - people who took growth hormone had higher lactic acid levels than those who did not, a sign of worse muscle fatigue.

"I am not surprised at all" by these findings, said William J. Evans, a physiologist at the University of Arkansas for Medical Sciences. A number of studies over the years have come to the same conclusion, he said in an e-mail.

The US Senate is considering a bill that would prohibit the sale of human growth hormone for illegitimate purposes. While parents of children with growth hormone deficiencies support stiffer penalties for abusers, they worry their access to the drug may be limited, according to the Magic Foundation, a group dedicated to helping children with growth disorders.