What do you know about testosterone replacement therapy?

Testosterone replacement therapy has gone from the doctor’s office to the center of a huge 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 US military will begin testing service members’ testosterone levels and make the replacement therapy available to those who qualify, saying the goal is to help troops function “at their absolute best.” The effort also builds on a larger campaign 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 ad puts a new focus on a treatment that has become increasingly popular in recent years, fueled by men’s health clinics, telehealth companies and online influencers, who promote testosterone boosting, or “T-maxxing,” as a way to address fatigue, aging and declining performance. Health and Human Services Secretary Robert F. Kennedy Jr. for 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 controversy over 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 eligible patients, including improvements in bone density and muscle mass, questions remain about the treatment’s long-term risks and its use among men without a clear medical need.

The concern is big: As many as one-third of men who take testosterone have not been formally diagnosed with low testosterone and may not benefit from treatment, according to the American Urological Association.

Doctors also stress that testosterone therapy is not a cure-all solution for low energy or normal aging. It’s generally reserved for men with clinically confirmed low testosterone, and experts say determining who qualifies requires more than one blood test — which appears to be the Army’s plan. Excess testosterone can also carry risks, including decreased sperm production.

“I’m not saying testosterone is bad. It’s good for people who need it,” said Dr. Adrian Sandra Dobbs, an endocrinologist at Johns Hopkins University School of Medicine. “But to replace it too much, 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 typically done through injections, gels, implantable pellets and oral medications, is intended for a more narrow demographic than social media might suggest.

Doctors say it’s generally reserved for men with clinically diagnosed hypogonadism — a condition in which the body doesn’t produce enough testosterone.

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

Low testosterone can result from several reasons, Dobbs said. While testosterone levels naturally decline with age, this alone is not usually considered a deficiency. Certain conditions can also inhibit testosterone production, including sleep disorders such as sleep apnea, damage to the testicles, pituitary gland disorders, some cancer treatments, and chronic diseases.

In some men, doctors may diagnose what is known as functional hypogonadism, where testosterone levels are low due to reversible factors such as obesity or chronic disease, even though the reproductive organs are structurally sound.

“Obesity, stress, fatigue and lack of sleep are very common and these conditions can reduce testosterone,” said Marcos Goncalves, MD, director of the Holman Division of Endocrinology, Diabetes and Metabolism at NYU Langone Health. “The right solution is to improve these aspects and allow testosterone to return naturally, but this is easier said than done.”

Goncalves added that diagnosing the condition usually requires more than one blood test.

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

Also, the result of low testosterone does not always mean that a person needs treatment. Testosterone levels can temporarily decrease during periods of extreme stress, illness, weight loss, or intense physical exertion, and may return to normal once these factors resolve, said Dr. Richard Ochs, a professor of internal medicine at the University of Michigan.

“It’s not easy to know if someone has enough testosterone and if this is a functional and reversible condition, or if this is a permanent, irreversible problem,” Okos said.

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

“I would say we try to limit treatment to people who we know will benefit,” Okos said.

For men with clinically confirmed low testosterone, 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’s unclear whether increasing testosterone in people who already have normal or only slightly low levels provides meaningful benefits for energy, cognition, athletic performance or overall health. They added that evidence supporting the use of testosterone as a broad-spectrum anti-aging or performance-enhancing treatment remains limited.

“It doesn’t make you smarter. It won’t make you a better pilot,” Dobbs said.

Even for fit patients, doctors say testosterone therapy carries risks and requires constant monitoring.

One concern is that the treatment could increase the number of red blood cells, which could thicken the blood and increase the risk of complications such as blood clots, NYU Langone’s Goncalves said.

While previous studies raised concerns that testosterone treatment may increase the risk of cardiovascular disease, 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 treatment compared with those who received a placebo.

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

He added that the treatment can also inhibit the body’s natural production of the hormone, reducing sperm production and possibly affecting fertility. Doctors generally discourage testosterone treatment in men who may want to have children.

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

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

Intense military training, sleep deprivation and prolonged physical exertion can temporarily suppress testosterone production, Goncalves said. In one study of US Marines who underwent survival, evasion, resistance, and escape training, or SERE, testosterone levels dropped by about half during the exercise before recovering afterward.

“There is no evidence of recovery [testosterone] He said that performance levels improved during that period, but he added that the question deserves study.

It also highlights the challenge facing any large-scale testing programme, some experts said. A low testosterone reading may not reflect a permanent deficiency that requires treatment, but rather a temporary response to difficult circumstances.

Okos also warned that testosterone treatment could create long-term problems for healthy service members. He said that because the treatment suppresses the body’s natural testosterone production, men who continue treatment for long periods may become dependent on it to maintain normal hormone levels.

This raises questions about what would happen if a service member receiving testosterone suddenly couldn’t get the treatment during a deployment or other military operation, Okos said.

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

“Testosterone will not make men more masculine or better fighters,” Dobbs said. “You need brains to win the war.”