No Evidence Growth Hormone Boosts Athletic Performance, Review Suggests

The team pooled data from previous studies in an attempt to summarize what’s known about growth hormone’s effects on athletic performance. Although this analysis may not reflect the way athletes actually take the drug illicitly, the lead author of the study, Hau Liu, MD, said with growth hormone in the news, it was a good time to scrutinize what was known about the drug.

Athletes’ use of growth hormone is banned by the International Olympic Committee, Major League Baseball and the National Football League. It is also illegal to distribute the drug for the purposes of sports enhancement in the United States. Despite this, athletes have been accused in recent months of taking the drug to boost their strength and performance. One attraction to growth hormone as an athletic enhancer is that it is difficult to detect.

But growth hormone may not deliver the benefits some athletes expect. “What we saw is that while there was a change in body composition, that didn’t translate to an improvement in performance,” said Liu, who was a clinical scholar in endocrinology at the time of the study.

The group searched the medical literature as far back as 1966 looking for studies that tested the physiological effects of excess growth hormone compared with a placebo in healthy people. To be included, the studies had to be double-blinded—neither the participants nor the researchers could know which participants received growth hormone and which received placebo. They excluded studies involving people with growth hormone deficits caused by pituitary tumors or other conditions. In those people, bringing growth hormone up to normal levels does improve strength.

They found 27 studies with a total of 303 participants that fit the bill. When they combined data from these independent studies looking at the effects of growth hormone in healthy people, the picture it painted wasn’t good for growth hormone.

Overall, people who received growth hormone did seem to have more lean body mass, which is generally associated with more muscle. However, during exercise the people who got growth hormone in some of the studies generated more lactate—the byproduct of exercise that can cause muscle fatigue. In one study, two cyclists who received growth hormone weren’t able to finish a workout because of fatigue.

Only two of the studies with a total of 38 participants looked at muscle strength in people who took growth hormone; they took it for six weeks in one trial, and 12 weeks in the other.

Despite having more lean body mass, the people didn’t appear to be any stronger after receiving the drug. Studies examining other measures of athletic performance, such as VO2max, which is a measurement of how much work the muscles can do, also revealed no improvement.

“The key takeaway is that we don’t have any good scientific evidence that growth hormone improves athletic performance,” said senior author Andrew Hoffman, MD, professor of endocrinology, gerontology and metabolism.

However, Hoffman urged caution in interpreting the data, given the embarrassment endocrinologists faced in the 1980s when they’d warned that testosterone had no performance-enhancing effects. Later studies testing doses at the levels athletes actually took clearly showed a performance boost from the drugs. With that in mind, the group is careful to warn that their findings only summarize the studies that have been done to date and may not represent the way athletes actually take the drugs.

The studies in this analysis examined people after only a single dose of growth hormone or up to three months of treatment; in all of the studies, the doses were lower than anecdotal reports of the doses athletes actually take. Athletes aren’t talking openly about how much of the hormone they take, but Liu said some estimates are that the illicit dose is as much as five times what was given in the studies. What’s more, athletes combine the hormone with other supplements, steroids and increased training, all of which could alter the effects of growth hormone.

Liu, who is now in the division of endocrinology and metabolism at the Santa Clara Valley Medical Center, said even if there’s no physiological data that growth hormone helps performance, it may still give athletes an edge psychologically. If an athlete appears more muscular, the boost in self-confidence from that alone might be enough to spur them to hit the baseball farther or cycle faster.

“So much of athletic performance at the professional level is psychological,” said Hoffman, who is also chief of endocrinology at the Veterans Affairs Palo Alto Health Care System.

Liu and Hoffman said that to learn the effects of real-world growth hormone supplementation, they would first need to know how much of the drug athletes were taking and for how long, on average. A large trial testing these doses in athletes would be difficult to conduct, they said. The side effects alone might make the trial ethically troublesome. The cost of growth hormone would also make the trial expensive unless companies donated the drug, which is unlikely.

The work will be published in the March 18 online version of the Annals of Internal Medicine and in print on May 20. Other Stanford researchers involved in the trial include senior research scientists Dena Bravata, MD, and Anne Friedlander, PhD; Ingram Olkin, PhD, professor emeritus of statistics; clinical fellows Vincent Liu, MD, and Brian Roberts, MD; medical fellow Eran Bendavid, MD, MPH; biostatistician Olga Saynina, MA, MBA; and Alan M. Garber, MD, PhD, the Henry J. Kaiser Jr. Professor.

The study was funded by the Agency for Healthcare Research and Quality, a National Research Service Award, Department of Veteran Affairs, Stanford University Medical Center, Stanford University, Genentech Inc., the National Science Foundation and the Evidence-Based Medicine Center of Excellence of Pfizer.