Many people will do almost anything to try to stave off aging--from undergoing painful nips and tucks to slathering on expensive creams to getting injections and downing pills that promise to erase wrinkles, lift sagging skin and keep the body forever young. One of the hottest anti-aging elixirs du jour is human growth hormone (GH), which has been touted for its supposed ability to do everything from build muscle to shave fat to thicken bones to lower cholesterol.

But beware: Eager as you might be to purchase youth in a bottle, a new study says there's zero scientific evidence that growth hormones are any more effective at turning back the clock than tap water or snake oil.

On the contrary: Researchers found that if taken by healthy adults it could cause a host of unhealthy side effects, including joint pain, soft tissue swelling, carpal tunnel syndrome, increased breast size in men, and a heightened risk of diabetes and pre-diabetes.

"Growth hormone should not be used for anti-aging purposes," says Hau Liu, a research fellow in endocrinology and health policy at Stanford University and author of the new study appearing in the January 16 issue of the Annals of Internal Medicine. "This costs hundreds to thousands of dollars a month and there is no scientific evidence supporting it and very real, potentially serious side effects."

Liu's team reviewed published studies of healthy senior citizens using growth hormones. At best, they found that the drugs increased lean body or muscle mass by slightly more than two kilograms (just over four pounds) and decreased fat mass by roughly the same amount. But Liu says the body changes did not translate into benefits: Longevity, bone density, cholesterol levels, stamina and blood sugar levels did not significantly change or improve.

"If you went to a gym pretty regularly, you might get that change without breaking into too much of a sweat," he says, "and you wouldn't spend $1,000 to $2,000 a month on something that appears to have minimal or no benefit and has the potential of some very serious side effects."

Liu notes that the biggest surprise was the dearth of data in this area, given the widespread popularity of GH as a supposed anti-aging therapy. In fact, he says, researchers reviewing scientific evidence found that there were only about 500 patients involved in rigorous controlled trials and that only a few more than 200 of them actually received growth hormones.

Human growth hormone is a protein naturally produced by the pituitary gland (at the base of the brain) that helps regulate growth during childhood and metabolism in adults. Production peaks during childhood and in the teen years and starts dipping at around age 30 and continues to decline into old age.

The Food and Drug Administration (FDA) has only approved the drug, now produced synthetically, to treat children with short stature (caused by growth hormone deficiency and some diseases and other growth problems)--and to treat adults who suffer from a growth hormone deficiency causing conditions like bone loss, high cholesterol and low energy.

The FDA bars pharmaceutical companies from marketing growth hormones for off-label uses such as anti-aging. But that hasn't stopped mostly Internet vendors from peddling--and thousands of people from snapping up--pills, sprays and injections supposedly containing GH as a passport to the Fountain of Youth. It is estimated that as many as 30,000 people in the U.S. used human growth hormone as an anti-aging agent in 2004, about 10 times as many as in the 1990s, despite the hefty price tag and the fact that it is not approved for such use.

Growth hormones took off as an anti-aging sensation in 1990 after a paper was published in the New England Journal of Medicine (NEJM) that presented the findings of a study involving a dozen men over age 60 injected with growth hormones three times a week for six months. At the end of the treatment, they had increases in lean body mass and bone mineral, unlike a group of nine men who had received no treatment.

The authors of that study did not make any claims that the treatment had reversed the aging process and stressed that more research was needed to draw any conclusions. But they did note that the increase in muscle and decrease in fat were "equivalent in magnitude to the changes incurred during 10 to 20 years of aging."

The statement attracted a heap of media attention, which triggered an explosion in use of growth hormones for anti-aging purposes. The NEJM tried but failed to quiet the hype with an editorial accompanying the article-- and one in 2003-- that warned against using growth hormones as an anti-aging therapy.

"My suggestion is that growth hormone should not be used for anti-aging," Liu says. "Rather than looking at growth hormone as a magic bullet or [ticket to] the fountain of youth, if you want to increase your chances of living a long and productive life, you should do the things that your moms and doctors always told you: Eat right, exercise often, get enough sleep, and don't smoke."