Testosterone therapy — widely advertised as a way to help men improve a low sex drive and reclaim diminished energy — might raise the risk of heart attack, according to new research.

The increased risk was found in men younger than 65 with a history of heart disease, and in older men even if they didn’t have a history of the disease. In both groups, heart attack risk doubled in the 90 days after the men began testosterone therapy, said researcher William Finkle, CEO of Consolidated Research, in Los Angeles.

The study was conducted by a research team that included experts from Consolidated Research, the U.S. National Cancer Institute and the University of California, Los Angeles. The included nearly 56,000 men who had been prescribed testosterone therapy — more than 48,000 of whom were under age 65. The risk for heart attack doubled in a 90-day period for men over 65 and those under 65 with a history of heart disease, the researchers found.

The two-fold increase in risk in younger men was seen only in those with a history of heart disease.

AbbVie and Actavis, the makers of testosterone therapies, did not respond to requests for comment on the study.

“Based on the best available data, testosterone replacement still appears to be safe … for properly selected patients,” said Dr. Ryan Terlecki, director of the Men’s Health Clinic at the Wake Forest Baptist Medical Center.

Among the flaws in the study, Terlecki said, was the use of information obtained from medical claims data, which makes it uncertain which men actually used the testosterone.

Terlecki said men who have a lack of energy should first see their doctor and ask about screening for depression and other conditions — such as thyroid disease or B12 deficiency — that could also be the cause.