According to a new study published in the New England Journal of Medicine (NJEM), testosterone replacement therapy was not associated with an increased risk of major cardiac events, such as heart attacks or strokes. However, health experts caution that these findings should not be used "as a justification for a more widespread use of testosterone in men," particularly those who are looking to feel younger or build muscle mass.

Testosterone therapy is safe for the heart, study finds

According to the New York Times, FDA has approved testosterone treatments for men who have low levels caused by medical conditions, such as hypogonadism, but doctors have also prescribed it for "off-label" use.

However, there have been concerns about testosterone's potential effect on cardiovascular health. In 2010, FDA halted a clinical trial of the hormone after patients started having heart attacks. In 2015, the agency required manufacturers to evaluate the potential risk of testosterone and added black box label to testosterone products to warn about the potential increased risk of heart attacks and strokes.

Now, a new large-scale clinical trial may assuage some patients' concerns about the hormone's cardiovascular risks. In the trial, 5,198 men ages 45 to 80 who were diagnosed with hypogonadism randomly received either a patch with a standard dose of testosterone or a placebo. All participants either had heart disease or were at a high risk of developing it.

After an average follow-up of two years, the researchers found that there was no difference in the rate of heart attacks, strokes, or cardiac death between the two groups. Around 7% of participants in both groups experienced some kind of cardiac event during the follow-up period.

However, researchers also identified other potentially serious complications from testosterone use. Participants who received testosterone therapy had a higher rate of irregular heartbeat, kidney problems, and blood clots in their legs compared to those who received the placebo.

Ultimately, "[w]e resolved one important question: Can we give testosterone to men with androgen deficiency to try to help them without harming them?" said Steven Nissen, chief academic officer at Cleveland Clinic's Heart, Vascular & Thoracic Institute and the study's senior author. "And the answer is, 'yes.'"

Health experts continue to caution against supplemental testosterone

Although the study's findings suggest that testosterone treatments may be safe for men with low levels of the hormone, Nissen warned that "these findings should not be used as a justification for widespread prescription," particularly among individuals who are taking supplements to feel younger or build muscle.

"Men want to feel like they felt at 18 to 25, with their sexual performance the way it was when they were youthful," Nissen said. "Some men see it as a potential fountain of youth and — unfortunately sometimes it is marketed that way. Men want to feel like Arnold Schwarzenegger did when he was 25. And that is not a reason to be taking it."

"Men want to turn back the clock," said William Schaffner, a professor of preventive medicine at Vanderbilt University Medical Center, who was not part of the study. "But low testosterone is not a life-threatening condition. You don't want to take any medication unless there is a reasonable chance you're going to benefit from it."

In addition, it's still unclear whether testosterone therapy is actually effective at treating low testosterone. Although there has been anecdotal evidence of benefits from both patients and providers, clinical trials of the hormone have shown much more modest benefits, if any at all.

"I think patients have this perception that it will improve their sexual function, will improve their mood and energy level," said Shalender Bhasin, an endocrinologist at Brigham and Women's Hospital and one of the authors of the current study. "But that's never been shown in a randomized clinical trial."

Overall, "[a]s cardiologists, we need to look at the benefits versus the risks, and this study will help us individualize therapy for our patients," said Beth Abramson, a professor of cardiac prevention and women's health at the University of Toronto, who was not involved in the study. "This doesn't mean that men with normal testosterone should be taking more of it." (Rabin, New York Times, 6/16; Edwards, NBC News, 6/16; Cimons, Washington Post, 6/16; Aubrey, "Shots," NPR, 6/16)