Testosterone Replacement Therapy: Benefits, Risks, and Who Actually Needs It

You feel tired in a way sleep doesn't fix. Your energy, your sex drive, maybe your mood and muscle all seem to have dimmed, and somewhere online you read that low testosterone could be the reason. Before you order a kit or ask for a prescription, it helps to understand what testosterone replacement therapy actually treats, who it's really for, and the trade-offs involved.

Testosterone replacement therapy (TRT) is a medical treatment that supplements low testosterone in men who have both low blood levels and real symptoms of deficiency. Done right, it's a carefully diagnosed, closely monitored treatment, not a quick fix or an anti-aging shortcut.

What is testosterone replacement therapy?

Testosterone replacement therapy restores testosterone in men whose bodies don't make enough. The medical name for that shortfall is male hypogonadism, or testosterone deficiency. TRT is FDA-approved specifically for conditions linked to a deficiency or absence of the body's own testosterone, not for healthy men hoping to boost normal levels.

Doctors generally divide low testosterone into two types. Primary hypogonadism comes from a problem in the testicles themselves, such as Klinefelter syndrome, mumps orchitis, testicular injury or torsion, or damage from chemotherapy. Secondary (also called hypogonadotropic) hypogonadism comes from a problem in the pituitary or hypothalamus, such as a pituitary tumor or radiation. The distinction matters because it shapes both the diagnosis and the right treatment plan.

Do I really have low testosterone? How it's diagnosed

This is the step people skip most often, and it's the most important one. A diagnosis of testosterone deficiency requires two things together: low testosterone on a blood test AND actual symptoms or signs. Low energy, low libido, erectile difficulty, fatigue, depressed mood, and reduced muscle mass are the kinds of symptoms doctors look for.

Major guidelines agree on a careful, repeat-tested approach. The American Urological Association uses a total testosterone level below 300 ng/dL as a reasonable cut-off, confirmed on two separate early-morning blood draws using the same lab and method. The Endocrine Society's 2018 guideline uses a slightly lower threshold of 264 ng/dL. Testing in the morning matters because levels naturally fluctuate through the day, and one borderline result is never enough on its own.

• AUA cut-off: total testosterone below 300 ng/dL
• Endocrine Society threshold: 264 ng/dL
• Confirm with two separate early-morning blood tests
• You also need symptoms or signs, not just a low number

How is TRT given? Injections, gels, patches, and pellets

There's no single way to take testosterone. The right form depends on your levels, your lifestyle, and how your body responds. According to Mayo Clinic, the main delivery options are injections, transdermal gels, skin patches, and implantable pellets placed under the skin.

One important caution: oral testosterone can cause serious liver problems and tends to produce uneven hormone levels, which is why doctors usually favor the other forms. Whatever method you use, TRT is not set-and-forget. Because many effects and side effects are tied to your blood level, regular monitoring is part of treatment.

• Injections - given on a scheduled basis
• Transdermal gels - applied to the skin daily
• Skin patches - worn and replaced regularly
• Implantable pellets - placed under the skin
• Oral testosterone - generally avoided due to liver risk and uneven levels

What are the benefits and risks of TRT?

For men with genuine hypogonadism, testosterone replacement can ease the symptoms that come with deficiency, including low sex drive, low energy, reduced facial and body hair, and loss of muscle and bone mass. Those are the situations TRT is designed for.

The risks are real and deserve equal attention. Many of them are dose-related, meaning they tend to track with how much testosterone is in your blood, which is exactly why monitoring matters. Reported risks include erythrocytosis (an overproduction of red blood cells), worsening sleep apnea, acne and skin reactions, gynecomastia (breast tissue growth), noncancerous prostate growth, and stimulation of existing prostate cancer. On heart safety, the large TRAVERSE trial offers the most useful recent data.

• Erythrocytosis (too many red blood cells)
• Worsening sleep apnea
• Acne and skin reactions
• Gynecomastia
• Prostate growth, and stimulation of existing prostate cancer
• Possible cardiovascular considerations (see below)

Is TRT safe for the heart?

Heart safety has been the biggest open question around TRT for years. The TRAVERSE trial, published in the New England Journal of Medicine in 2023, was designed to address it directly. It enrolled 5,246 men aged 45 to 80 who had symptoms of hypogonadism along with existing or high cardiovascular risk, and randomly assigned them to testosterone gel or placebo for a mean treatment of about 27 months.

The headline finding was reassuring: testosterone was noninferior to placebo for major adverse cardiac events, meaning cardiovascular death, nonfatal heart attack, and nonfatal stroke. But the trial wasn't entirely clean. The testosterone group had higher rates of atrial fibrillation, acute kidney injury, and pulmonary embolism. The takeaway is nuanced rather than a green or red light, and it's a conversation to have with a clinician who knows your full history.

When should I see a doctor?

If you have ongoing symptoms like low energy, low libido, or unexplained fatigue, that's a reason to get evaluated rather than self-diagnose. A clinician can confirm whether your testosterone is genuinely low, look for an underlying cause, and weigh whether TRT is appropriate for you.

TRT also isn't right for everyone. Guidelines advise against starting it in men who are planning to have children soon, since testosterone can impair fertility, and in men with breast or prostate cancer, certain prostate findings, severe urinary symptoms, uncontrolled heart failure, a very recent heart attack or stroke, or a high hematocrit. Seek urgent care for chest pain, sudden shortness of breath, leg swelling, or stroke symptoms at any time. The right path here is individual, and getting a proper workup and a personalized plan from a clinician is worth far more than any number off a home test.