Oct 25 (Reuters) - Drugs used to treat low testosterone will carry a new warning about the potential risk of abuse, the U.S. Food and Drug Administration said on Tuesday.

The warning is the latest in a series of actions the agency has taken to try to curb prescriptions of a product whose use has soared over the past decade, especially among middle-aged men.

Last year the agency told drug makers to clarify that the products are approved only for men with specific medical conditions and that they may increase the risk of heart attacks and strokes.

The new warning, the agency said, “will alert prescribers to the abuse potential of testosterone and the serious adverse outcomes, especially those related to heart and mental health.”

The consumer watchdog Public Citizen previously petitioned the FDA to add a boxed warning - the most serious possible - about the risk of heart attacks and other cardiovascular problems. The agency has stopped short of that.

Testosterone therapy is approved for men who lack or have low testosterone in conjunction with associated medical conditions, such as a genetic failure of the testicles to produce testosterone.

Symptoms of low testosterone can include loss of libido, depression, decreased muscle mass and fatigue.

Prescriptions for “Low T” have soared over the past decade, driven by a surge in use by men facing natural declines in testosterone levels as they age. According to the FDA, the number of men prescribed tetosterone jumped more than 75 percent to 2.3 million between 2009 and 2013.

Research by Public Citizen found that almost 25 percent of men prescribed testosterone did not previously have a blood test to determine if their level was low.

The more than $2 billion market for testosterone treatments includes skin patches, short-acting injections and topical gels and is dominated by AbbVie Inc’s AndroGel and Eli Lilly & Co’s Axiron.

Testosterone is an anabolic steroid that can be abused by adults and adolescents, including athletes and body-builders.

“Reported serious adverse outcomes,” the agency said, “include heart attack, heart failure, stroke, depression, hostility, aggression, liver toxicity and male infertility.” (Reporting by Toni Clarke in Washington; Editing by Bernard Orr)