The FDA warns that prescription testosterone is only approved for use in men with low testosterone levels due to certain medical conditions.

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Wladimir Bulgar/Getty Images/Science Photo Libra

The FDA warns that prescription testosterone is only approved for use in men with low testosterone levels due to certain medical conditions.

Wladimir Bulgar/Getty Images/Science Photo Libra

Year 2014 time The magazine ran a cover story titled menopause? !documenting the rise of the $2 billion testosterone industry that markets the hormone as a way to ward off age-related declines in sexual function, energy and strength.

As interest has soared, so have questions about safety. A small study has shown that testosterone can improve muscle strength in older men, but it has also found something unexpected: a higher rate of adverse cardiovascular events, such as heart attacks. In 2015, the FDA required manufacturers to add warning labels to inform consumers of potential risks. The use of prescription testosterone began to decline.

Now, a new study published Friday may reassure those interested in the treatment. Men who had low testosterone levels and took prescription testosterone gel to boost their sex hormone levels did not have a higher rate of heart attack or stroke than men who took a placebo, the study found.

“The results of this study provide reassuring substantive evidence that, when properly prescribed, testosterone replacement therapy does not significantly increase the risk of death from cardiovascular causes,” said study author Dr. Michael Lincoff of the Cleveland Clinic.Results will be published in New England Journal of Medicine.

(This study did not evaluate over-the-counter dietary supplements containing testosterone, which are not regulated like drugs.)

The new study was designed to better understand the impact of testosterone on cardiovascular risk, explained senior study author Dr. Steven Nissen, a cardiologist at the Cleveland Clinic. However, he interpreted the results cautiously.

“While the trial showed some evidence that testosterone therapy may be safe for men with low testosterone, these findings should not be used as a reason for widespread prescribing,” Nissen said.

The FDA says the treatment should be reserved for men with low testosterone levels confirmed by lab tests. Nissen said he was “concerned” that the results might be interpreted by bodybuilders and athletes as a green light for testosterone use by those hoping to improve their performance. “I really think it’s a potential risk,” Nissen said.

Nissen emphasized that all participants had cardiovascular disease or were at high risk for cardiovascular disease as well as symptoms of hypogonadism, the medical term for the inability to produce enough testosterone. The study included about 5,200 men aged 45 to 80 who were assigned either a placebo gel or a testosterone gel rubbed into the skin daily for 22 months.

Seven percent of men who used testosterone gel had a major cardiac event, such as a heart attack or stroke. Among the placebo group, 7.3 percent had a major cardiac event. And, given that all participants were at high risk for heart disease, the results showed that testosterone did not increase the risk. While that may be reassuring, Nissen points to other safety concerns identified during the study, including an increased risk of cardiac arrhythmias in men taking testosterone.

“We didn’t expect this to happen,” Neeson said. In addition, there was a slightly increased risk of kidney injury and pulmonary embolism. The study authors concluded that the findings “support current guidelines that testosterone should be used with caution” in men with previous thrombotic events.

The study was funded by a group of testosterone manufacturers, including AbbVie, maker of Androgel, the product used in the study. Common side effects and risks associated with the product are covered in marketing materials, including a possible increased risk of prostate cancer. In the new study, 12 patients (0.5%) in the testosterone and placebo groups developed prostate cancer, compared with 11 patients (0.4%) in the placebo group. The trial was run independently by the Cleveland Clinic Clinical Research Coordinating Center.

The new findings are “very encouraging,” said Dr. Kambiz Tajkarimi, a board-certified urologist in Washington, D.C., who treats patients with sexual dysfunction. He prescribes testosterone to many of his patients, including pills marketed as bioidentical hormone replacement therapy, and says he uses it himself.

“I’m so tired,” said Tajkarimi, who is in his early 50s. Now, he says he has more energy, which he attributes to the testosterone pills. “I think it’s a really beneficial treatment.”

However, clinical trials of testosterone have shown modest or even substantive relief of symptoms, or benefits of testosterone replacement therapy. One of the key findings of the new study is that about 60 percent of men in clinical trials stopped taking testosterone for the duration of the trial, said Dr. Steven Woloshin of the Dartmouth Institute for Health Policy and Clinical Practice. Many said their symptoms persisted.

“It’s just another way of saying it doesn’t work or isn’t effective enough [men] Notice the benefits,” Woloshin said.

Previous studies, including one published in 2016, have shown that testosterone can improve sexual function and mood in men 65 and older, but a closer look at previous studies reveals very limited benefits, Woloshin said. For example, a 0.6-point improvement on a 13-point sexual function scale and a 0.5-point improvement on a 45-point mood scale “are unlikely to be noticed by many men,” says Woloshin. Also, fatigue did not improve.

Overall, Woloshin said he is also concerned that the findings could reignite interest in testosterone replacement therapy for people who might not benefit from it. “It’s not the fountain of youth,” Woloshin said. “You feel the effects of aging.”

Neeson agrees. “Men want to feel like they did when they were younger,” he said. But, of course, we cannot turn back the clock.