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Barry Bonds is one sweet swing from tying Hank Aaron's immortal home run record, but purists want an asterisk by his name because of allegations that he has used performance-enhancing drugs. Amid allegations of testosterone and blood doping, some of the favourites in this year's Tour de France were forced to withdraw from the race.

There are, of course, differences between these superathletes and the average aging male, but not as many as you think.

Every day, men walk into clinics like mine and say, "I've lost my mojo," or "my golf drive is down," or "my trainer sent me," and ask to have their testosterone levels tested. Aging men, like star athletes, don't want to lose. They want a fix.

Our testosterone levels decline over time, as do our hearts, brains, erections and bones. But does this mean that taking testosterone enhances our performance as we age? Certainly some of my patients think so. I am much less sure. Let me explain why.

Testosterone therapy has been around for years, but was primarily reserved for men with a severe deficiency, or hypogonadism, that stems from a problem such as a genetic disorder or a tumour in a gland. According to a report by the Institute of Medicine, a U.S. advisory body, sales of testosterone in the United States had been about $18-million until 1998.

But by 2002, many aging men started to wonder whether testosterone was a fountain of youth (the hormone's use skyrocketed) - it had become a $400-million business that has grown every year since.

Some doctors feel that testosterone therapy in the aging male is a no-brainer. They would argue that they are treating partial androgen deficiency in the aging male (PADAM), otherwise known as male menopause. The theory is that, similar to women and estrogen (although less precipitously), men's production of testosterone declines after the age of 50. Testosterone replacement therapy (TRT) offers a possible panacea as the hormone affects bone, muscle, brain, and most or least importantly, libido and erectile health. Testosterone has usually been given as an injection, occasionally as a pill, but now the medical journals are full of ads for new formulations of testosterone such as gels and patches.

Let's start with the diagnosis of PADAM. Many men are tested for their total testosterone, but the current thinking is that 98 per cent of it is inactive anyway and bound to protein, and the "free" or "bioavailable" 2 per cent is what counts. Guidelines published last year in the Journal of Clinical Endocrinology & Metabolism point out that 30 per cent of men found to have an abnormal result go on to have a normal result in a second test.

Also, there is no clear consensus of what is a normal level for men over 50, since our standard is based on men under 40. It is estimated that more than 50 per cent of men over 50 have reduced testosterone levels.

A pharmaceutical executive would see this as a huge market, but I wonder if we aren't manufacturing a disease for what is simply a fact of nature. I have learned in my medical career, with much trial and error, not to screw with nature.

What about the effectiveness of testosterone? In 2004, the Institute of Medicine conducted a review of testosterone therapy studies in older men and concluded that because of study limitations, "assessments of risks and benefits have been limited and uncertainties remain about the value of this therapy in older men."

Whether it concerned depression, heart or bone health, or erectile function, the trials reviewed by the IOM were all of low quality, prone to error and showed mixed results. New trials, hopefully of better quality, are under way.

So it may work, may not, my patients say, but "what's the harm?" The downside of TRT is as inconclusive as the upside. These trials, often with only 20 men in them and rarely with more than 100, were simply not large enough and did not last long enough to assess harm. The biggest fear remains theoretical: that TRT could accelerate prostate and even breast cancer. Other side effects that need more evaluation include thickening of the blood, worsening sleep apnea and enlarging prostate.

One can't help but consider the roller coaster women have been through on their own hormone replacement therapy, which uses estrogen. The story of HRT in women has lessons on the hierarchy of research trials, the hubris of medicine and whether we should be manipulating the natural course of aging.

First we pushed it on every woman. Then we said don't stop if you're already taking HRT, but don't start. Then we said don't start at all. Now we say that the evidence shows a slight overall disadvantage in taking HRT, but that some women with significant symptoms may have a better quality of life on HRT and may want to take the calculated risk. One thing for sure is that the amount of research on HRT is much more abundant than that on TRT.

My own advice is to watch the TRT story unfold from the sidelines. I am particularly biased by the lack of safety data at this point. My clinical experience is that mojo can be helped by more boring interventions such as improved partner communication and work-life balance.

Barry Bonds may disagree, but there you go.

Michael Evans is an associate professor at the University of Toronto and staff physician at Toronto Western Hospital.