In an effort to curb the growing number of men taking testosterone, the U.S. Food and Drug Administration (FDA) has taken a series of actions to warn men taking testosterone of the many dangers associated with the hormone.

The latest action came last year in late October when the FDA approved a class-wide labeling change for all prescription testosterone products, such as AndroGel, Testim, Axiron and Fortesta.

“The new Warning will alert prescribers to the abuse potential of testosterone and the serious adverse outcomes, especially those related to heart and mental health that have been reported in association with testosterone/AAS abuse,” the FDA warned Oct. 25.

Some of the serious adverse effects reported to the FDA related to testosterone include heart failure, stroke, depression, hostility, liver toxicity, male infertility and a bevy of other injuries.

In its warning, the FDA reiterated that prescription testosterone products should only be used as hormone replacement therapy by men who have low testosterone due to medical conditions. Some men, for example, cannot produce enough of the hormone if chemotherapy or infections damage the testicles or because of genetic problems.

The number of men taking testosterone has skyrocketed over the past decade. According to one 2013 study, the number of men prescribed the hormone more than tripled since 2001.

While some men do require hormone replacement therapy, that study in the journal JAMA Internal Medicine found that a quarter of men did not even have their levels tested before being prescribed the hormone.

FDA Expresses Growing Concern About Testosterone Abuse

The October warning from the FDA is just another in a long string of actions to curb abuse of the hormone.

In April 2015, the FDA announced it was requiring manufacturers of prescription testosterone products to clarify the approved uses of the medications as well as add warnings about a possible increased risk of heart attacks and strokes in patients taking the hormone.

The FDA again said it should only be prescribed to men with disorders of the testicles, pituitary gland or brain that may cause low testosterone.

“However, FDA has become aware that testosterone is being used extensively in attempts to relieve symptoms in men who have low testosterone for no apparent reason other than aging,” the FDA said in the 2015 drug safety communication. “The benefits and safety of this use have not been established.”

Between 2009 and 2013, the number of men prescribed testosterone shot up more than 75 percent, according to the FDA. Some men have been prescribed the hormone to address the loss of testosterone that happens naturally with aging.

While there is evidence that the hormone is being prescribed more liberally by some healthcare professionals, the hormone is also abused by adults and adolescents who use it to improve how they look or their sports performance.

Testosterone Also Target of Class-Action Lawsuits

The combination of more men being prescribed the hormone and an increased risk of heart failure and stroke from testosterone has resulted in thousands of lawsuits filed against the makers of testosterone products.

Plaintiffs are suing Abbott, AbbVie, Pfizer and others over claims that the drugs resulted in injuries like heart attack, stroke, pulmonary embolism and more. A multidistrict litigation was created by a federal panel in 2014 that consolidated more than a thousand cases from plaintiffs contending similar injuries.

“On the basis of the papers filed and hearing session held, we find that these actions involve common questions of fact, and that centralization of all actions in the Northern District of Illinois will serve the convenience of the parties and witnesses and promote the just and efficient conduct of this litigation,” the panel wrote in 2014.

More recently in September, U.S. District Judge Matthew Kennelly selected eight testosterone cases to move forward as bellwether trials. These cases will help guide how the courts will find subsequent lawsuits, rather than hearing the thousands of pending cases.