Thousands of American men use testosterone gel to boost energy and improve libido. Soon it will be available over here. But, asks Oliver Bennett, do British men really need this?

Around five years ago, 55-year-old Geoff Lammert felt listless. An IT worker in a City of London bank, he could hardly be bothered to walk upstairs. "I felt tired, sweaty and miserable," says Lammert. "When I went for tests, they told me my testosterone was low." Off he went for testosterone implants at Harley Street, and bang: the life force came rushing back, via a £770 six-month slow release capsule embedded in his right buttock.

Now Lammert - who features in Thursday's Channel 4 documentary Testosterone: Are You Man Enough? - is an advocate of this hormone replacement therapy (HRT). "I'm not saying it's for everyone. But it gives me a real lift. I call it my rocket fuel." He adds that it has re-awoken his libido, energy and assertiveness, and even claims effects that verge on the miraculous. "If I cut myself, I heal quicker. My eyes are better. It really seems to slow the ageing process." Meanwhile, other testosterone users have reported that colours seem brighter, that their minds are clearer and that their spatial abilities are enhanced.

Most of us know about testosterone. Its properties - drive, risk-taking, assertiveness, competitiveness, territoriality, aggression, lust - are the essence of the qualities we understand as "maleness". And it's now available in supplementary form, gaining a reputation as the very elixir of youth. Any of the estimated 600,000 British men with low testosterone levels that read the litany of indicators - sagging sex drive, low energy, depression, dwindling muscle mass and bone density - would be interested. Plus, there is the additional cosmetic lure of increased muscle definition.

In the US, some have hailed it as a wonder drug. "This could end middle age for men," Christopher Steidle of the Indiana University School of Medicine has said. "We think it is a medical miracle that will be a multi-billion dollar industry."

Over there, it is already on the consumer market. In 2000 it hit the market in the easily-deliverable form of gels with names like Androgel, Auxilium and Testim, and is pitched at ageing baby boomers. A two page advertisement in Time magazine recently showed a car's fuel gauge at empty. "Fatigued? Depressed mood? Low sex drive? Could be your testosterone is running on empty." Sales of testosterone gels and patches in the US doubled last year, and of course, there's a huge pharmaceutical push behind it.

Now the testosterone boom is beginning here, albeit in a more cautious way. In two weeks a testosterone gel called Testagel will come onto the medical circuit. "We're trying not to publicise it and we certainly won't hype it up," says Alison Slingsby, product manager for drug company Scherings. "It's for clinical use only, to be prescribed by an endrocrinologist where testosterone production is too low."

Women have had HRT for years, argue the advocates: why not men? Testosterone has already been enshrined in British television drama 40, where Eddie Izzard's mid-life character self-administered testosterone jabs in his rump. There have been injections, implants and patches to be placed on the shaved scrotum, a method popular in Germany. "Uptake has been poor in the UK because of the delivery methods," says Pierre Bouloux, an endrocrinologist at the Royal Free Hospital. "But I think the gel - which is applied to the torso and which you wash off after a couple of hours - could popularise it." After all, the market took off in the US when the gels came on.

One of the best known advocates of male HRT is Dr Malcolm Carruthers, a "consultant andrologist" with a practice in London and the author of The Testosterone Revolution (Harper Collins, £14.99). He claims that half of all men in their fifties have low testosterone levels which they could boost with HRT, and he believes it is efficient at resolving the problems of the "andropause": that is, the male menopause. "Testosterone has a lot to offer," he says. "I've seen lots of men that have watched their businesses and families fall apart due to low energy and they benefit greatly from this kind of treatment." But Carruthers adds a note of caution. "I'm bothered that it's got this macho image, associated with virility and power. I'd rather link it to vitality and energy levels."

Certain sections of the medical establishment are far more nervous about the ethical and medical implications. "It does some good things and some bad things," says Pierre Bouloux, endocrinologist at the Royal Free Hospital. There is a raft of possible side effects, from prostate problems possibly leading to cancer, the stimulating of red blood cell production possibly leading to heart attacks and strokes, liver damage and other conditions. And people respond to testosterone in varied ways. "Individual thresholds are vastly different," says Bouloux. "One of the misunderstandings is that it's a linear response. It's not." Anyone taking testosterone now is frankly a bit of a guinea pig, and Bouloux points to the risks of HRT for women - including increased possibility of heart attacks, strokes and cancer, which have led many doctors to resist prescription. The same is likely to be the case for testosterone.

Another factor that makes some professionals nervous of testosterone is that it has the potential to come onto the consumer rather than the medical market. "It's typical of our times that medical treatments end up being used for quality of life or cosmetic purposes," says Nick Neave, lecturer in hormones and behaviour at Northumbria University. "Testosterone, which is being marketed as the latest 'fountain of youth', is bound to go that way."

It is vastly oversimplified, says Neave. "We don't fully understand how it works. The way it's perceived is too deterministic, and I don't think it's been thought through. People don't only respond to hormones."

It also raises the nightmare scenario - as Neave puts it - "of 60 and 70 year olds fighting in lap dancing clubs". In the documentary, Lammert tells of how testosterone re-awoke the dangerous teenager within, and he raced a motorbiker through Southend-on-Sea. "It's a serious down-side, particularly if you're old and your body isn't up to it." Which is why Lammert reckons it should only be used carefully and under strict medical supervision.

Lammert has also found another weird side effect. "Every so often, I feel a burst of power in my blood. You know when the Incredible Hulk bursts out of his clothes? It's like that. I have to sit and wait for it to pass." There's also the problem of dependence. It replaces the body's normal production of testosterone, and one can experience symptoms of withdrawal upon stopping a course. Before Lammert needs another implant, he feels depleted. "You feel heavy. You plod up the stairs. It's like Superman and green Kryptonite."

This is unlikely to bother many of its new users, who include women, who take it for the same reasons men do - power, energy, assertiveness, and raised sexuality. Indeed, there's a special testosterone gel for women called LubiGel being trialled in the US. "Women taking testosterone should expect virilising behaviour," says Bouloux. These can include a hairy face and nipples, pimples, enlarged clitoris, deep voice, and increased sexual desire. Tantasisingly, the film says that a high profile woman working at the House of Commons uses it.

The testosterone revolution could, as Nursing Standard has suggested, be "a triumph of pharmaceutical marketing over need" and a treatment without a disease. It's undoubtedly driven by the fear of ageing, and the subtle, contemporary tyranny that demands optimum performance. Those looking at the bigger picture have criticised it as part of the artificial medicalisation of the ageing process. But Lammert is prepared to take the testosterone risk. "I'd rather have ten good years than 30 years feeling like Victor Meldrew."

'Testosterone: Are You Man Enough?' is on Channel 4, Thursday at 11.15pm