Testosterone therapy is coming to the U.S. military. Here's what doctors say we know — and don't know — about it

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.

Who is the therapy intended for?

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.

A low testosterone result also does not always mean someone needs treatment. Testosterone levels can temporarily decline during periods of severe stress, illness, weight loss, or intense physical exertion and may return to normal once those factors resolve, said Dr. Richard Auchus, professor of internal medicine at the University of Michigan.

"It's not that easy to tell whether someone is sufficient in testosterone and whether that is kind of a functional and reversible situation, or if that is an irreversible permanent problem," Auchus said.

What are potential benefits and risks?

The benefits of testosterone replacement therapy can be real for the right patients.

"I would say that we try to limit the treatments to people we know are going to benefit," said Auchus.

For men with clinically confirmed testosterone deficiency, treatment can increase sex drive, improve erectile dysfunction, help restore muscle mass and bone density, and boost energy levels and mood. It can also improve bone mineral density, reducing the risk of osteoporosis and fractures in men with low hormone levels.

But experts say it is less clear whether raising testosterone in people who already have normal or only mildly low levels provides meaningful benefits for energy, cognition, athletic performance or overall health. Evidence supporting testosterone as a broad anti-aging or performance-enhancing treatment remains limited, they added.

"It doesn't make you any smarter. It won't make you a better pilot," Dobs said.

Even for appropriate patients, physicians say testosterone therapy carries risks and requires ongoing monitoring.

One concern is that the treatment can increase red blood cell counts, potentially thickening the blood and raising the risk of complications such as blood clots, NYU Langone's Goncalves said.

While earlier studies raised concerns that testosterone therapy might increase cardiovascular risk, more recent evidence has been reassuring. A major 2023 trial – the largest and most comprehensive to date – found no higher rate of heart attack, stroke or cardiovascular death among men receiving testosterone therapy than among those given a placebo.

Researchers did observe higher rates of certain conditions, including atrial fibrillation, acute kidney injury and pulmonary embolism, underscoring the need for careful patient selection and monitoring.

The treatment can also suppress the body's natural production of the hormone, reducing sperm production and potentially affecting fertility, he added. Physicians generally discourage testosterone therapy in men who may want to have children.

Other potential side effects include acne, breast tenderness or enlargement, fluid retention and worsening symptoms of untreated sleep apnea.

How might this apply to the military?

The military's plan to test service members' testosterone levels raises a key question: How should doctors interpret hormone levels in people undergoing extreme physical and psychological stress?

Goncalves said that intense military training, sleep deprivation and prolonged physical exertion can temporarily suppress testosterone production. In one study of U.S. Marines undergoing Survival, Evasion, Resistance and Escape, or SERE, training, testosterone levels fell by roughly half during the exercise before recovering afterward.

"There is no evidence that restoring [testosterone] levels during that period improves performance," he said, though he added that the question would be worth studying.

That also highlights a challenge for any large-scale testing program, some experts said. A low testosterone reading may not reflect a permanent deficiency requiring treatment, but rather a temporary response to demanding conditions.

Auchus also cautioned that testosterone therapy can create long-term issues for otherwise healthy service members. Because treatment suppresses the body's natural testosterone production, men who remain on therapy for extended periods may become dependent on it to maintain normal hormone levels, he said.

Auchus said that raises questions about what could happen if a service member receiving testosterone were suddenly unable to access treatment during a deployment or other military operation.

More broadly, experts say testosterone replacement therapy should not be viewed as a shortcut to improved military performance.

"Testosterone is not going to make men more macho or better fighters," Dobs said. "You need brains to win a war."