"It doesn't look like it helps, and there's a hint of evidence it may worsen athletic performance," said Dr. Hau Liu, of Santa Clara Valley Medical Center in San Jose, Calif., who was lead author of the review.
Growth hormone, or HGH, is among the performance enhancers baseball stars Roger Clemens and Andy Pettitte were accused of taking in the blockbuster Mitchell Report. Clemens denies using the hormone, while Pettitte admits using it.
But the new research has some limitations and sheds no light on long-term use of HGH. The scientists note their analysis included few studies that measured performance. The tests also probably don't reflect the dose and frequency practiced by athletes illegally using the hormone. Experiments like that aren't likely to be conducted.
"It's dangerous, unethical and it's never going to be done," said Dr. Gary I. Wadler, a member of the World Anti-Doping Agency and a spokesman for the American College of Sports Medicine.
Consequently, those in the field have to depend on such reviews or "what we hear on the ground," he added.
Human growth hormone is made by the pituitary gland and promotes growth. A synthetic version has been available since the 1980s and its use is restricted for certain conditions in children and adults, including short stature, growth hormone deficiency and wasting from AIDS.
Although banned for other uses, growth hormone has been used by a variety of athletes and was cited along with steroids as one of the performance-enhancing drugs abused by baseball players in the report in December by former Senate majority leader George Mitchell. Several athletes, including Pettitte, have said they used HGH while recovering from an injury, an issue not covered in the review.
"There are a lot of claims that it's this wonder drug," said Liu.
Wadler said one of the appeals of growth hormone for athletes is that it can't be detected in a urine test. A blood test will be available soon, and another is in development, he said.
"They think they are getting a free ride -- they aren't getting a drug test," he said. "They believe they are stronger and bigger."
Liu and his colleagues at Stanford University sought to find out if growth hormone really could improve performance. They looked for the best published tests, those comparing participants who got the hormone to those who didn't get the treatment.
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They analyzed 27 studies involving 440 participants. The results
were released Monday by the Annals of Internal Medicine.
Researchers found that those who got the hormone put on about 5
pounds more of muscle, and lost about 2 pounds more of fat, although
the fat loss wasn't statistically different. The researchers said
some of the extra body mass could just be fluid buildup.
There was no difference found in strength or exercise stamina
between the two groups, but there were only two strength studies and
eight that measured exercise. Those who got the hormone had more
side effects including swelling and fatigue.
The review couldn't consider long-term effects, since the longest
study was three months, and most were much shorter.
The researchers also said the doses used in the research may be
lower than those used by athletes, who may be combining growth
hormone with other performance-enhancing drugs.
Dr. Alan Rogol of the University of Virginia and the Indiana
University School of Medicine, said the work was a good review but
had to rely on inadequate research.
"There are just tons of things we don't know," said Rogol.
The California researchers had support from Stanford, government
agencies and Genentech Inc., which makes growth hormone; none of the
groups had a role in the study. Two researchers also have been
consultants or received grants from Genentech and other drugmakers.
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