While growth hormone adds some muscle, it doesn't appear to improve strength or exercise capacity, according to a review of studies that tested the hormone in mostly athletic young men.
"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 Mitchell Report. Clemens denies using the hormone, while Pettitte admits that he used it.
But the new research 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. Those types of experiments likely would not 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.
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.
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, he said.
Liu and his colleagues at Stanford University 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 five pounds of muscle.
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.