There is no proof that growth hormone therapy makes people live longer, say US scientists.
Therapy had no significant clinical benefit
The therapy has been touted in some quarters as a way to prevent - or even reverse - ageing.
However, a Stanford University team found no evidence that it had any more effect than a regular mild workout.
In fact the Annals of Internal Medicine study found the therapy posed a risk of side effects, including swollen joints, carpel tunnel syndrome and diabetes.
Lead researcher Dr Hau Liu said: "There is certainly no data out there to suggest that giving growth hormone to an otherwise healthy person will make him or her live longer.
"We did find, however, that there was substantial potential for adverse side effects."
Growth hormone is naturally produced by the pituitary gland, a pea-sized organ at the base of the brain.
Production falls off
Production is highest during childhood and adolescence, but typically starts to taper off from around the age of 30.
The hormone is given to short children and adults whose pituitary glands do not produce enough to maintain normal metabolism.
However, it is also widely promoted as an anti-ageing therapy on the web.
A small 1990 study in the New England Journal of Medicine seemed to suggest that the therapy could in effect turn back the clock.
Researchers found men injected with growth hormone gained extra muscle, and bone density, and lost fat.
Although the researchers admitted their study was far from definitive, they suggested the effect was "equivalent in magnitude to the changes incurred during 10 to 20 years of ageing."
At the same time the journal published an editorial warning against the general use of growth hormone as a therapy in adults.
But despite this, and subsequent repeated attempts to play down the findings, the popularity of growth hormone as an anti-ageing therapy has continued to grow.
It is estimated that up to 30,000 people in the US alone used it for this purpose in 2004.
The Stanford team reviewed 31 studies in which growth hormone was used to treat elderly people, with no significant health problems, other than being slightly overweight.
They found growth hormone had a modest effect on body composition, increasing muscle by slightly more than 2kg and decreasing body fat by roughly the same amount.
However, it had no impact on bone density, cholesterol levels, or the rate at which the body used oxygen.
Dr Liu said: "In short, the studies provided no real evidence that the therapy resulted in increased fitness."
Professor John Wass, of the University of Oxford, who is chairman of the British Society for Endocrinology, said the therapy potentially had a role to play in treating elderly people who were deficient in the hormone.
For instance, there was some evidence to suggest it might improve memory.
However, he added: "If you are not growth hormone deficient all the data suggests that it is not a good idea to take it."
Dr Peter Trainer, an endocrinologist at Manchester's Christie Hospital, agreed.
He said: "This is a very reputable group who have come to a conclusion which most serious endocrinologists would believe.
"If you give people growth hormone it does help to build up muscle bulk and lose fat, but that does not necessarily translate into feeling better, or younger, or being able to perform better."
Dr Trainer said growth hormone had been tested as a treatment for people in intensive care, who tend to waste away. The results showed that it doubled their death rate.
He said there was a danger that it would do people more harm than good.