TUESDAY, Aug. 11, 2015 (HealthDay News) -- Testosterone therapy may not be as bad for men's heart health as previously thought, but it doesn't seem to turn back time on their sex lives either, a new trial shows.

"That was the surprising thing," said senior study author Dr. Shalender Bhasin, director of the Boston Claude D. Pepper Older Americans Independence Center at Brigham and Women's Hospital in Boston. "Many middle-aged and older men take testosterone because they feel it will improve their sex life, but the study showed that men who had low-normal or slightly low levels did not show any improvement."

Testosterone therapy has become big business in the United States, as baby boomers seek ways to counter the effects of aging, Bhasin said.

Sales of testosterone amounted to around $20 million a year in the early 1990s, but by 2012 it had grown into a $2 billion industry, he said.

However, recent studies have cast a pall on testosterone therapy, indicating it may increase risk of heart attacks and strokes, said Bhasin, who also serves as director of the hospital's Research Program in Men's Health: Aging and Metabolism.

The U.S. Food and Drug Administration in March started requiring all prescription testosterone products to carry a label warning about possible increased risk of heart attacks and strokes.

"Testosterone has become a blockbuster drug," he said. "It's just extraordinary growth, and there's been growing concern among the regulatory agencies about the potential for the increase in risk of cardiac events."

To assess the safety and effectiveness of testosterone treatment, Bhasin and his colleagues enrolled 308 men older than 60 with testosterone levels in the low or low-normal range, or about what you'd expect in normally aging males.

As men age, their testosterone levels naturally decline, on average by 1 percent a year after age 40, researchers said. Testosterone, a hormone primarily secreted by the testicles, plays a key role in male reproduction, muscle growth, bone mass and body hair.

About half the men were provided daily testosterone gel packets, which they rubbed into their skin. The other men were given a placebo gel that contained no medicine. The research was supported by drug manufacturers Solvay Pharmaceuticals Inc. and Abbvie Pharmaceuticals, which provided the testosterone gel.