TORONTO -- The use of replacement testosterone therapy among older men in Ontario has jumped dramatically over the last 15 years, despite a lack of evidence that the therapy is safe or effective.

The study, published online Wednesday in the journal PLOS ONE, found the number of prescriptions for testosterone replacement therapy dispensed to men aged 66 and older rose 310 per cent between 1997 and 2012. In all, 28,477 men received the drug during the research period.

"In 2012, we found that approximately one of every 90 older men in Ontario was being treated with a testosterone product, which is very high," said lead author Tara Gomes, a scientist at the Institute for Clinical and Evaluative Sciences and St. Michael's Hospital in Toronto, the centres that conducted the study.

Yet only about six per cent of the men had a diagnosis of hypogonadism -- a condition in which the body doesn't produce enough testosterone, the main indication for the treatment and the only one that allows the drug's cost to be reimbursed by Ontario's drug plan.

Prescriptions for TRT, as the treatment is known, were originally covered by the plan with no restrictions. But in 2006, the province limited coverage to those diagnosed with hypogonadism, which typically arises due to a problem with either the testes or the brain's pituitary gland, both of which are responsible for testosterone production.

"We did see an initial drop in the use of the products, four to six months after this policy came into place, but it quickly changed direction after that time, and by 2010 the rates had far exceeded what they were at any other previous point in the study period," said Gomes.

TRT has been aggressively promoted by drug companies as a treatment for a reduction in the hormone due to aging, which can cause a loss of libido, lack of energy, reduced muscle mass, mood swings and disturbed sleep.

"There have been some really major marketing campaigns for 'low T' or 'andropause,' which basically are names for age-related hypogonadism that are being used to highlight this issue for older men," said Gomes.

While direct-to-consumer drug marketing isn't allowed in Canada, pharmaceutical companies often obliquely promote their products through TV ads and websites that encourage consumers with certain symptoms to talk to their doctors.

"So when you go on those websites, they have quizzes that men can take where they can answer questions as to whether or not they've had decreased libido, reduced energy, mood swings and falling asleep after dinner, for example," she said. "And if they answer yes to several of these questions, they're directed to speak to their physicians about receiving tests for low testosterone.

"And this has obviously created a demand and an awareness of some medicalization of the aging process, and a demand for testosterone products that I think is likely driving a lot of the trends that we're seeing."

Yet, Gomes said the push for men to seek out hormone replacement is concerning because some recent studies have suggested that TRT may raise the risk of heart attack, stroke and other cardiovascular problems in some men.

In response to that research, Health Canada issued an advisory Tuesday, saying the department is updating safety information about the 12 brand-name and generic TRT products approved for sale in this country. While inconclusive, the studies raise the question of whether the treatment might cause potentially serious, or even fatal, harm.

Other jurisdictions, including the United States, have also seen spiralling rates of prescriptions for replacement testosterone, and the Food and Drug Administration in that country is also reviewing TRT products' safety.

Gomes said increased prescribing rates in Ontario -- and likely the rest of Canada -- have largely been driven by topical testosterone, a gel formulation that's absorbed through the skin. While use of pill and injectable forms of the hormone have remained relatively static, topical testosterone has become the most popular type of TRT since it was listed on the provincial drug formulary in 2005.