Drugmakers should conduct new trials to assess the heart risks of testosterone therapies used by 2.3 million men last year, U.S. regulatory advisors said.

A Food and Drug Administration advisory panel voted 20-1 that drug developers should further assess the cardiovascular risks of testosterone products, with 16 panelists saying it should be studied only in some situations, Morgan Liscinsky, an FDA spokeswoman, said in an e-mail after the meeting.

The advisors also voted 20-1 yesterday that the agency should revise who should be prescribed the drugs, Liscinsky said. The panel said little evidence exists that testosterone replacement therapies are effective for treating low levels of the hormone caused by aging, the Associated Press reported.

Use of testosterone products from AbbVie Inc., Eli Lilly & Co. and others almost doubled in 2013 from 2010. About 20 percent of patients on the treatments don’t have laboratory evidence showing they need them, according to an analysis of data that FDA staff members called “particularly concerning” in briefing documents.

A study published in November suggested that testosterone replacement drugs boost the odds of a heart attack, stroke or dying by 29 percent. Other studies offered conflicting results, showing a decreased risk of mortality among testosterone users.

The panel’s recommendations would shrink the pool of patients eligible to take testosterone supplements, while drugmakers would have to conduct more testing to determine whether the drugs pose cardiovascular risks. The agency isn’t required to follow its panels’ advice.

“Testosterone replacement therapy is an important men’s health topic. AbbVie is committed to our patients and we will work with the FDA during its review,” the North Chicago, Illinois-based company said in a statement.

Lilly in an e-mailed statement said that based on its assessment, current evidence does not support a causal link between testosterone therapy and serious cardiovascular events. “However, based on feedback from the committees, Lilly will collaborate with the FDA to determine how to communicate cardiovascular risk to patients,” it said.

Blockbuster Product

Last year, market leader AbbVie reported $1.04 billion in sales of Androgel, a topical gel used to treat low testosterone. Auxilium Pharmaceuticals Inc. gained $271 million in 2013 for its Testim gel and Testopel, testosterone pellets implanted under the skin.

FDA advisers are scheduled today to consider a new testosterone product. Closely held Clarus Therapeutics Inc. is seeking approval for Rextoro, which would be the first oral testosterone medicine in 50 years, according to the company.

Increasing Use

While testosterone replacement therapy has been approved in the U.S. since 1950 for men with medical conditions leading to deficiencies, such as testicular damage due to chemotherapy, more men who have low testosterone for no other reason than age are using the products, the FDA said in documents.