It is touted as the fountain of youth: the hormone testosterone, which some men say helps them build muscle, lose weight and gain energy.

In the United States, prescriptions for testosterone therapy have increased significantly in the past 10 years, according to a study in JAMA Internal Medicine.

The study found that 50 per cent of the men who received testosterone therapy had lower than normal levels of testosterone.

But around 25 per cent did not have their testosterone levels tested before starting the treatment.

In Australia, there has been a similar increase in men using testosterone, particularly with the introduction of two new testosterone products: a long-acting injection and a gel.

Dr David Handelsman, from the Anzac Research Institute, found that testosterone prescribing increased in all states and territories from 1992 until 2010.

The latest figures from the pharmaceutical benefits scheme show the number of men using long-acting testosterone injections has almost doubled.

Dr Handelsman is concerned about the increase.

"It's wasteful, it's misguided, it's not rational prescribing," he said.

"The risks are accelerating cardiovascular disease and accelerating prostate disease. The risks are not facts yet but they are very good reasons to be cautious."

'I feel fantastic'

But American patient Chris Running, 57, says testosterone is a wonder drug, helping him to lose weight and gain muscle.

"When I look in the mirror and I feel frigging fantastic," he said.

There are legitimate reasons for men to use testosterone.

Men suffering androgen deficiency or a condition called Klinefelter syndrome can be prescribed it as a treatment.

But Dr Handlesman says there has been no increase in men being diagnosed with that condition.

Instead he says it is being promoted with "speculative, non-approved indications such as andro-pause (male menopause) or male sexual dysfunction".

He says there is a growing overuse of the hormone as an anti-ageing tonic and to boost sexual function.

"It is highly marketable with an easily confected popularity which creates a demand that bypasses sound clinical practice," he said.

Testosterone replacement therapy (TRT) is being looked at in clinical trials as a potential treatment for a range of conditions including obesity and diabetes.

Preliminary results in a study by the Prince Henry Institute in Melbourne in 2010 into the use of TRT in aging and obese men found that participants experienced a reduction of body fat and improved muscle mass.

Trial underway to treat diabetes

The trial involved 40 obese middle-aged men who were monitored over a year to identify changes in abdominal fats and risks of cardiovascular diseases.

Dr Carolyn Allan led the clinical trial in 2010 and says it was a promising pilot study.

Dr Allan and her team are now part of a trial that is currently underway in Western Australia, South Australia, Victoria and New South Wales looking into how testosterone treatment can be used to prevent type 2 diabetes in overweight men.

The study is looking for men who do not have any adverse factors, such as higher risk of prostate disease.

She says that they are also only working with men who have lower than expected testosterone levels for their age.

The aim of the trial is to see if men who are at risk of diabetes, who are obese and have low testosterone levels, can be treated with a weight-watchers program, as well as testosterone.

"We are not looking at men who already have healthy testosterone levels," she said.

Men interested in being involved in the study can find out more here.