"That is a substantial percentage, and it is across the population," Baillargeon said.
About 50 percent of the men receiving testosterone therapy during that time period had hypogonadism, a condition where a man is unable to produce normal levels of testosterone - defined as 300 to 1,000 nanograms per deciliter of blood.
But the study also found that 25 percent of the newest testosterone users were being treated without having their blood level checked.
"I don't know what exactly is happening in the clinic visit, but to prescribe this treatment without accessing a baseline testosterone level, and to see that it is happening among 25 percent, is concerning, particularly since we don't know the long-term risks of this," Baillargeon said.
What is happening, say some medical professionals, is a large dose of salesmanship. Testosterone is being promoted on television, radio, and the Internet as the way for middle-aged men to put the zip back in their step, from the boardroom to the bedroom. According to Consumer Reports, companies spent $14 million advertising prescription testosterone treatments in 2011 and $100 million in 2012.
The return on that investment was more than $2 billion in sales last year, a 90 percent increase in the last five years, according to IMS Health, a healthcare technology and information company. Easy-to-apply gels, such as Androgel, Testim, Fortesta, and Axiron, were the fastest-growing segment of the market.
"I can't make a direct correlation with these data," Baillargeon said. "I think people can make inferences about the prescribing patterns. I think those kind of speak for themselves."
Testosterone therapy is safe and does work for men with hypogonadism.
"There is no controversy about whether or not a man who has low testosterone production due to pituitary disease or testicular disease should be treated with testosterone," said Peter J. Snyder, a specialist in male reproductive endocrinology at the University of Pennsylvania. "That is well-accepted."
But testosterone therapy for men with normal levels is a waste of money. In fact, a man with a normal testosterone count taking hormone treatments turns off his natural production. Once the therapy is stopped, it can take two months to a year before natural production resumes. In the meantime, the man will feel terrible and be infertile.
"If someone has normal testosterone, then taking more of it is no benefit," Snyder said. "That wouldn't benefit that man in the slightest. So if you say to me testosterone has certain pros, then I would say that you have been watching too much television."
There are some concerns about health risks for men taking testosterone therapy. One is high blood-cell count that could lead to stroke and heart attack. Another worry is prostate cancer.
"You can get an increase in blood counts with testosterone therapy," said Dr. Kenneth Varano, who specializes in Natural Bioidentical Hormone Therapy and owns BodyLogicMD in King of Prussia. "We regularly keep an eye on PSA tests. It should be monitored."
Snyder is coordinating the Testosterone Trials, a National Institutes of Health study that is examining whether the gradual decline of testosterone in men is a normal or abnormal result of age.
Unlike women who experience a precipitous drop in hormones during menopause, men see a gradual decline in testosterone. One reason the decline may be abnormal, Snyder said, is the striking parallels of older men with low testosterone and younger, hypogonadal men. Both groups experience a range of symptons, including an increase in body fat, a loss of energy, and a decreased sex drive.
"There have been some studies to try to find out if you give old men testosterone, will those things get better," he said. "There are hints that things get better. But the results have not been clear-cut."
Robert Calandra can be reached at 215-836-0101 or firstname.lastname@example.org.