Men who partake in testosterone therapy have an increased risk of experiencing a heart attack, stroke or death, a new study finds.

The study done at the Veterans Affairs Eastern Colorado Health Care System and published in the Journal of the American Medical Association found that the veterans included in the study that were undergoing testosterone therapy had a 30% higher risk for an adverse cardiovascular event, which is causing doctors to question the safety of testosterone therapy.

“Prior to this study, we didn’t know much about the cardiovascular risk,” said Michael Ho, lead researcher and senior author of the testosterone study. “Men taking testosterone have to ask themselves whether the risks are worth the benefits they may be receiving.”

Researchers looked at the health records of 8,709 men who had low testosterone levels and also had a coronary angiography, which is a test that looks for plaque buildup in blood vessels among patients, between 2005 and 2011 in the VA health system. The study compared men in that group who were undergoing testosterone therapy to those who weren’t.

It primarily looked at men who had significant health problems to begin with such as blocked arteries, high blood pressure and diabetes as well as men who averaged 60 years of age. It is not certain if what the study found also applies to healthier men.

“It does kind of raise the question of, maybe when patients and their physicians are thinking about starting testosterone therapy, potential risks such as the ones we looked at should be in that discussion,” Ho added.

Beyond the cardiovascular problems, a study done at the Stanford University School of Medicine published in December 2013 found that men who have testosterone levels that were too high displayed a poor immune response to the vaccine designed to prevent influenza. The study concluded that too much testosterone can slow down the immune system overall.

Men Taking Testosterone without Being Tested

Testosterone therapy is used to treat sexual dysfunction, increase bone density, increase strength and lean muscle mass as well as help lower cholesterol and reduce insulin resistance.

Testosterone therapy has soared in recent years. In 2008, there were 208 million prescriptions for testosterone supplements. By 2012, the number of prescriptions more than doubled, reaching 432 million.

A different study done at the University of North Carolina at Chapel Hill found that many men are now being prescribed testosterone, who appear to have normal testosterone levels.

“Over the past decade, older and middle-aged men are increasingly being tested for low testosterone levels and being prescribed testosterone medications, particularly in the United States,” said J. Bradley Layton, author of the study. “While direct-to-consumer advertising and the availability of convenient topical gels may be driving more men to seek treatment, our study suggests that many of those who start taking testosterone may not have a clear medical indication to do so.”

Testosterone levels fall naturally as men age. However, younger men can also experience a drop in testosterone due to certain medical conditions. There is a difference in opinion on which men should be treated.

The National Institute of Health was conducting a study in 2009 of about 200 frail older men who were taking testosterone and had already developed heart disease, when researchers were forced to stop the study due to the fact that too many of the participants were having heart attacks.

In contrast to the findings in the Colorado VA study, a study in 2012 that looked at 1,031 Veterans Health Administration patients revealed that there was a 39% lower risk for heart disease and death among men who were undergoing  testosterone therapy.