The two most popular hormones are DHEA and pregnenolone, steroid hormones that convert other substances into sex hormones. The claims made on their behalf are dramatic.
More than 2,000 studies in the US suggest DHEA has wide-ranging beneficial effects: combating cancer and obesity, improving memory, reversing ageing and boosting libido. It is also thought to protect against Alzheimer's, narrowing of the arteries and osteoporosis.
The pill forms of DHEA are synthesised from Mexican yams by genetic engineering techniques, though some forms of the pills are thought to be manufactured from mares' urine.
An estimated 20 million Americans are believed to take one of the many "social" hormone replacement pills. Although DHEA is unlicensed in the UK, it is available in health food and drug stores in the US where it is considered a food supplement.
In the UK, DHEA - its full name is dehydroepiandrosterone - and other "wonder pills" are controlled drugs and can only be supplied by doctors on a named-patient basis. But those who want to get the pills need take only a short flight into cyberspace, where they will discover dozens of websites for DHEA mail-order companies. Under schedule four of the Misuse of Drugs Act, it is not an offence to possess DHEA for personal use.
There are side-effects, particularly when the correct dose is exceeded. These include hair growth in women, skin blemishes, aggression and a drop in good cholesterol levels. It may also bring to light existing, latent prostate cancers.
"Any scientist who claims these pills will keep you active until the age of 120 is talking nonsense," said Dr Jagadish Chakraborty, senior lecturer in chemical biochemistry at the University of Surrey.
"When claims like this are made that a drug can do everything, I become a little bit suspicious. DHEA is a powerful compound with very potent side-effects if the dose is exceeded."
Drugs such as DHEA and pregnenolone should only be taken under supervision, said Dr Chakraborty. "The fear is control. It's going to be difficult for doctors to know what their patients are taking."
John Moran, however, medical director of the HMC Harley Medical Clinic in London, was so impressed by the effect it had on his patients that he tried it himself.
He started taking DHEA 18 months ago following a life-threatening case of septicaemia. He is in no doubt about the benefits it has brought. "I feel more energised, have more stamina, an increased sex drive and it has lifted the mild depression I was suffering," he said.
Dr Moran, has given it to more than 100 patients. Most of those he treats are aged 40 or more. "Men and women come to me complaining of low energy levels, less sex drive and impaired short-term memory. Some are irritable and depressed.
"If I establish their DHEA level is low I can look to raise it by prescribing DHEA." A course typically lasts three months and involves a 25mg daily dosage for men and a 5mg dosage for women, usually in the form of a pill dissolved under the tongue.