Last December's Mitchell Report described the widespread use of steroids and growth hormone by professional baseball players. Even though it's illegal to use growth hormone for any purpose other than to treat people with deficient production of the hormone, these ballplayers risked their reputations in an effort to improve their performance.

But the Mitchell Report did not address a crucial question: Do steroids and human growth hormone actually improve athletic performance? This is a pressing matter, since professional ballplayers are by no means the only athletes who are experimenting with these powerful substances today.

For this reason, I was initially excited to see that a recent article in the Annals of Internal Medicine was described as saying "growth hormone doesn't boost performance." The article included a systematic review of short-term, randomized, controlled trials that had examined the effect of growth hormone in 440 participants between the ages of 13 and 45. I was hoping this review would establish that growth hormone did not enhance athletic performance. Alas, I was disappointed.

The study involved two groups of participants, one which got growth-hormone injections and another which did not (the control group). Compared with the control group, those taking growth hormone gained an average five pounds in lean body mass - an increase that's often assumed to be due to the growth of additional muscle.

But the authors of this article determined - at least in the two studies they reviewed where strength was measured - that weight increases in the growth hormone group were not associated with increased strength. This led the authors to believe that their gain in body mass was merely due to fluid accumulation, and not to muscle growth.

And the article's findings about growth-hormone injections got worse (or better if, like me, you'd like to see an end to athletes using these drugs): the researchers found that those getting growth hormone had more side effects than did the control group, including fatigue, joint pain, and soft-tissue edema (fluid accumulation). The growth-hormone group was also disproportionately affected by carpal tunnel syndrome (pain, weakness, or numbness in the hand and wrist due to pressure on the median nerve as it passes through a narrow tunnel in the wrist).

The problem with this study is that it reviewed only short-term clinical trials, ones in which the average duration of growth hormone use was only 20 days, and none that lasted more than three months. These time intervals are much too short to allow for a definite resolution of this issue.

So, it is still possible that longer use or larger doses of the hormone might indeed improve muscle strength and athletic performance. Unfortunately, it seems unlikely that any controlled trial will soon (or ever) be launched to determine whether growth hormone injections provide any benefits for athletes.

In the meantime, the data do at least suggest that growth hormone does not help an athlete to "bulk up" and outdo his or her competitors. And so athletes, especially those in high school and college, would be wise to avoid injecting illegal growth hormone.