The clinics insist there are few, if any, side effects from HGH. Mainstream medical authorities say otherwise.
A 2007 review of 31 medical studies showed swelling in half of HGH patients, with joint pain or diabetes in more than a fifth. A French study of about 7,000 people who took HGH as children found a 30 percent higher risk of death from causes like bone tumors and stroke, stirring a health advisory from U.S. authorities.
For proof that the drug works, marketers turn to images like the memorable one of pot-bellied septuagenarian Dr. Jeffry Life, supposedly transformed into a ripped hulk of himself by his own program available at the upscale Las Vegas-based Cenegenics Elite Health. (He declined to be interviewed.)
These promoters of HGH say there is a connection between the drop-off in growth hormone levels through adulthood and the physical decline that begins in late middle age. Replace the hormone, they say, and the aging process slows.
"It's an easy ruse. People equate hormones with youth," said Dr. Tom Perls, a leading industry critic who does aging research at Boston University. "It's a marketing dream come true."
Some scientific studies of HGH have found modest benefits: some muscle and bone building, as well as limited fat loss, but nothing like the claims of the anti-aging industry. And some of the value credited to HGH may instead come from testosterone, which is routinely provided with HGH by anti-aging doctors and sports suppliers.
Endocrinologists say it's natural for the body to produce less growth hormone as people age beyond their early 20s, because they aren't growing anymore. Only a tiny number of adults with extraordinarily low HGH levels — perhaps several thousand of them — are believed to suffer real deficiencies that can properly be treated with the hormone.