What you need to know about testosterone replacement therapy

Testosterone replacement therapy has moved from the clinic to the center of a huge cultural phenomenon focused on performance, longevity, and men’s health.

Now, the therapy is back in the spotlight after Secretary of Defense Pete Hegseth announced last week that the U.S. military would begin testing testosterone levels in service members and make replacement therapy available to those who qualify, saying the goal is to enable troops to perform 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 therapy made by pharmaceutical companies such as AbbVie, Pfizer and Marius Pharmaceuticals.

The announcement puts new focus on a treatment that has become increasingly popular in recent years, promoted by men’s health clinics, telemedicine companies and online influencers who promote testosterone, or “T-maxxing,” as a way to combat fatigue, aging and performance decline. Secretary of Health and Human Services Robert F. Kennedy Jr. has also promoted testosterone therapy as part of his anti-aging regimen.

According to healthcare research firm IQVIA, prescriptions rose from 7.3 million in 2019 to more than 11 million in 2024. But the safety of taking synthetic forms of testosterone, a hormone that influences sex drive, mood, and other health factors, has long been debated.

Although some studies have shown it to be effective in qualifying patients, including improving bone density and muscle mass, questions remain about the therapy’s long-term risks and its use in men without a clear medical need.

This concern is significant because up to one-third of men who take testosterone have never been formally diagnosed with testosterone deficiency and may not benefit from treatment, according to the American Urological Association.

Doctors also emphasize that testosterone therapy is not a universal solution to low energy or normal aging. The test is typically aimed at men with clinically confirmed testosterone deficiency, and experts say multiple blood tests are needed to determine who is eligible, which appears to be the military’s plan. Excess testosterone can also come with 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 you have to be very careful about replacing it with too much.”

As testosterone therapy becomes the new national topic, doctors say what we know and don’t know about its benefits, risks, and who should consider treatment.

Testosterone replacement therapy, commonly delivered through injections, gels, implantable pellets, and oral medications, is aimed at a more limited group of people than social media suggests.

Doctors say this is usually limited to men with clinically diagnosed hypogonadism, a condition in which the body doesn’t produce enough testosterone.

This generally means a persistent drop in testosterone levels, along with symptoms such as decreased sex drive, fatigue, erectile dysfunction, depressed mood, decreased bone density, and loss of muscle mass and strength.

Dobbs said there are several possible causes for low testosterone. Testosterone levels naturally decline with age, but that alone is usually not considered a deficiency. Certain conditions can also suppress testosterone production, including sleep disorders such as sleep apnea, testicular damage, pituitary gland disorders, some cancer treatments, and chronic illnesses.

In some men, doctors may diagnose so-called functional hypogonadism, in which reversible factors such as obesity or chronic disease cause low testosterone levels even though the reproductive organs are structurally intact.

“Obesity, stress, fatigue, and lack of sleep are very common, and these conditions can lower testosterone,” said Marcus Gonsalves, director of the Holman Division of Endocrinology, Diabetes, and Metabolism at NYU Langone Health. “The right solution is to improve these aspects and restore testosterone naturally, but that’s easier said than done.”

However, Gonsalves added that diagnosing the condition typically requires multiple blood tests.

Because testosterone levels fluctuate throughout the day, medical guidelines generally recommend two separate blood draws in the morning to confirm low levels and evaluate patients for potential causes before considering treatment, he said.

Also, just because your testosterone levels are low doesn’t necessarily mean you need treatment. Dr. Richard Orcas, a professor of internal medicine at the University of Michigan, says testosterone levels can temporarily drop during periods of severe stress, illness, weight loss, or strenuous exercise, but can return to normal once those factors are resolved.

“It’s not so easy to determine whether a person has enough testosterone and whether it’s a functional, reversible situation or a permanent, irreversible problem,” Orcas says.

The benefits of testosterone replacement therapy are real for the right patient.

“I would say we’re trying to limit the treatment to people we know will be effective,” Orcas said.

For men with clinically confirmed testosterone deficiency, treatment increases libido, improves erectile dysfunction, restores muscle mass and bone density, and improves energy levels and mood. It also improves bone density and reduces the risk of osteoporosis and fractures in men with low hormone levels.

But experts say it’s less clear whether raising testosterone in people who already have normal or mildly low levels will have a meaningful effect on energy, cognition, athletic performance and overall health. Evidence supporting the effectiveness of testosterone as a broad-based anti-aging or performance-enhancing treatment remains limited, they added.

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

Doctors say that even in suitable patients, testosterone therapy carries risks and requires continued monitoring.

One concern is that the treatment may increase the number of red blood cells, making the blood thicker and increasing the risk of complications such as blood clots, said Gonsalves, of NYU Langone.

Previous studies have raised concerns that testosterone therapy may increase cardiovascular risk, but more recent evidence is encouraging. A major trial in 2023, the largest and most comprehensive to date, found no higher rates of heart attack, stroke, or cardiovascular death in men receiving testosterone therapy than in men given a placebo.

Researchers have observed a higher incidence of certain diseases, such as atrial fibrillation, acute kidney injury, and pulmonary embolism, highlighting the need for careful patient selection and monitoring.

The treatment also suppresses the body’s natural production of hormones, which can reduce sperm production and affect fertility, he added. Doctors generally do not recommend testosterone therapy for men who may want to have children.

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

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

Gonsalves said intense military training, lack of sleep and long hours of physical labor can temporarily suppress testosterone production. One study of U.S. Marines undergoing Survival, Evasion, Resistance, and Escape (SERE) training found that their testosterone levels dropped by about half during training and then recovered.

“There is no evidence that restoring (testosterone) levels during that period improves performance,” he said, but added that the issue would be worth studying.

This also highlights challenges for large-scale testing programs, some experts say. Low testosterone readings may reflect a temporary response to a severe condition rather than reflecting a permanent testosterone deficiency that requires treatment.

Orcas also warned that testosterone therapy can cause long-term problems in healthy military personnel. Because the treatment suppresses the body’s natural production of testosterone, men on long-term treatment may become dependent on testosterone to maintain normal hormone levels, he said.

Orcas said the question arises what happens if a military member receiving testosterone suddenly loses access to treatment during a deployment or other military operation.

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

“Testosterone doesn’t make men more muscular or better fighters,” Dobbs says. “It takes brains to win wars.”