What to know about testosterone replacement therapy as the U.S. military plans to test troops

Testosterone replacement therapy has shifted from the doctor's office to the center of a massive cultural phenomenon focused on performance, longevity and men's health.

Now, the treatment is back in the spotlight after Defense Secretary Pete Hegseth announced last week that the U.S. military will begin testing service members' testosterone levels and make replacement therapy available to those who qualify, saying the goal is to help troops operate at their "absolute best." The effort also builds on a larger push by the Trump administration to promote and expand public access to testosterone replacement therapies, which are made by pharmaceutical companies such as AbbVie, Pfizer and Marius Pharmaceuticals.

The announcement puts a new focus on a treatment that has grown increasingly popular in recent years, fueled by men's health clinics, telehealth companies and online influencers, who promote testosterone, or "T-maxxing," as a way to address fatigue, aging and declining performance. Health and Human Services Secretary Robert F. Kennedy Jr. has also touted testosterone therapy as part of his anti-aging regimen.

Prescriptions rose from 7.3 million in 2019 to more than 11 million in 2024, according to healthcare research firm IQVIA. But there has long been a debate around the safety of taking synthetic forms of testosterone, the hormone that affects sex drive, mood and other health factors.

While some research has shown benefits for patients who qualify, including improvements in bone density and muscle mass, questions remain about the therapy's long-term risks and its use among men without a clear medical need.

The concern is significant: up to a third of men taking testosterone have never been formally diagnosed with testosterone deficiency and may not benefit from treatment, according to the American Urological Association.

Physicians also stress that testosterone therapy is not a universal solution for low energy or normal aging. It is generally intended for men with clinically confirmed testosterone deficiency, and experts say determining who qualifies requires more than a single blood test — which appears to be the military's plan. Excess testosterone can also carry risks, including reduced sperm production.

"I'm not saying that testosterone is bad. It is good for people that need it," said Dr. Adrian Sandra Dobs, an endocrinologist at the Johns Hopkins School of Medicine. "But to overreplace it – we have to be very careful about that."

As testosterone therapy enters a new national conversation, here's what doctors say we know – and don't know – about its benefits, risks and who should consider treatment.

Testosterone replacement therapy, which is commonly administered through injections, gels, implantable pellets and oral medications, is intended for a more narrow population than social media may suggest.

Physicians say it's generally reserved for men with clinically diagnosed hypogonadism – a condition in which the body does not produce enough testosterone.

That generally means persistently low testosterone levels alongside symptoms such as reduced sex drive, fatigue, erectile dysfunction, depressed mood, low bone density, or loss of muscle mass and strength.

Dobs said low testosterone can stem from several causes. While testosterone levels naturally decline with age, that alone does not typically qualify as a deficiency. Certain conditions can also suppress testosterone production, including sleep disorders such as sleep apnea, damage to the testicles, pituitary disorders, some cancer treatments and chronic illnesses.

In some men, doctors may diagnose what's known as functional hypogonadism, in which testosterone levels fall because of potentially reversible factors such as obesity or chronic disease, even though the reproductive organs are structurally intact.

"Obesity, stress, fatigue, and poor sleep are very common and these conditions can reduce testosterone," said Marcus Goncalves, director of the Holman Division of Endocrinology, Diabetes and Metabolism at NYU Langone Health. "The correct solution is to improve those aspects and let testosterone naturally come back up, but that is easier said than done."

But diagnosing the condition typically requires more than a single blood test, Goncalves added.

Because testosterone levels fluctuate throughout the day, medical guidelines generally recommend confirming low levels with two separate morning blood draws and evaluating patients for potential underlying causes before considering therapy, he said.