The Food and Drug Administration is warning doctors against the overuse of testosterone-boosting drugs for men, saying the popular treatments have not been established as safe or effective for treating common signs of aging like low libido and fatigue.
 

The agency says drugmakers must clarify that their drugs, currently taken by millions of U.S. men, are only approved to treat low testosterone levels caused by disease or injury, not normal aging.

Additionally, the FDA warned that the drugs may increase the risk of heart attack, stroke and other cardiovascular problems. Drugmakers must add information about that potential risk to their warning labels and conduct a long-term study to examine the issue, the FDA said.

The federal rebuke follows years of industry marketing for new pills, patches, gels and injections that promise relief from low testosterone or "Low-T." Promotions from AbbVie, Eli Lilly & Co. and others link the condition to a variety of ailments common to aging men, including sexual problems and low mood.

The advertising blitz for drugs like AbbVie's Androgel and Lilly's Axiron has pushed sales of testosterone drugs to over $2 billion. Roughly 2.3 million U.S. patients filled a prescription for testosterone in 2013, up 77 percent from 2010, according to FDA figures.

The heading on Abbvie's Androgel website reads: "You are a man. You want the facts. You get down to business. You might have low testosterone."

North Chicago-based Abbvie said in a printed statement that the company "is committed to our patients and we continue to work with the FDA."

Testosterone injections were first approved in the 1950s for men who had been diagnosed with hypogonadism, a form of abnormally low testosterone caused by disorders of the testicles, brain and other hormone-related organs.

But current labeling on the drugs is vague enough that companies have been able to promote their drugs to millions of otherwise healthy men who simply have lower-than-normal levels of testosterone.

"The benefits and safety of this use have not been established," the FDA said in a statement Tuesday.

While men's testosterone levels naturally decline after age 40, experts disagree on whether that drop actually leads to the issues like decreased energy and lower bone density.

Additionally, testosterone levels change by the hour and are affected by a range of environmental factors, such as stress and sexual arousal.

The FDA began reviewing the safety of testosterone drugs last January after two federal studies associated the drugs with increased rates of heart attack, stroke and other serious problems. But other studies have associated testosterone with increased longevity.

Companies sell prescription testosterone in a variety of forms. The market leader, Androgel, is a gel applied to the shoulders and arms. Lilly's Axiron is a solution that rolls on like deodorant. Endo Pharmaceuticals sells a long-acting injectable testosterone called Aveed.