Understanding Testosterone Replacement Therapy

Testosterone replacement therapy (TRT) gets a lot of attention online, and not all of it is accurate. This guide explains what TRT actually treats, how a low-testosterone diagnosis is made, which treatment formats are FDA-approved, and what realistic benefits, risks, and monitoring look like. It is educational, not medical advice; decisions about TRT belong with a licensed clinician working from your blood test results.

What TRT is, and what it is not

Testosterone is a hormone made mainly in the testes that supports sexual function, bone density, muscle mass, red blood cell production, and more. TRT supplies testosterone to treat hypogonadism, a medical condition in which the body does not produce enough of it. The Endocrine Society and the FDA are clear that testosterone is approved for men who have low testosterone together with an associated medical condition.

What TRT is not: it is not an anti-aging treatment, a guaranteed route to more muscle or energy, or an appropriate response to the normal, gradual decline in testosterone that can come with age. In men with normal testosterone, supplementation generally offers little benefit.

How low testosterone is diagnosed

A diagnosis requires more than symptoms. Clinical guidelines recommend diagnosing hypogonadism only when a man has both consistent symptoms and unequivocally low testosterone confirmed by blood work. Because levels swing through the day and from day to day, testosterone is measured on two separate mornings while fasting, using a reliable assay. A total testosterone consistently below 300 ng/dL is a commonly cited threshold, interpreted alongside your overall health.

Diagnosis often includes follow-up testing to find the underlying cause, since low testosterone can stem from treatable issues such as obesity, thyroid problems, sleep apnea, certain medications, or pituitary conditions. Men 40 and older are typically screened with a baseline PSA before starting therapy.

FDA-approved formulations

There is no single best delivery method; the choice depends on your clinician's assessment, your preferences, and how closely you can be monitored. Approved options include:

• Injections – intramuscular or subcutaneous, on a weekly or longer schedule
• Topical gels – applied daily, with care to avoid skin-to-skin transfer to others
• Transdermal patches – worn on the skin and changed daily
• Pellets – implanted under the skin by a clinician, releasing over months
• Buccal and oral – a system applied to the gum, plus oral testosterone undecanoate (such as Jatenzo, Tlando, and Kyzatrex)

Benefits and risks, honestly

For men with genuinely low testosterone, the most consistent benefit is modest improvement in sexual function and libido. Effects on energy, mood, bone density, and body composition are more variable. Set expectations accordingly, and be skeptical of any source promising uniform, dramatic results.

Risks are real and are the reason supervision matters. They include increased red blood cell production (which can raise clot risk), worsening of sleep apnea, acne, breast enlargement, reduced sperm production and fertility, and prostate growth. In 2025 the FDA also required a class-wide label warning that testosterone products can raise blood pressure. Clinicians generally advise against TRT for men planning fertility soon, or with a history of prostate or breast cancer, untreated severe sleep apnea, uncontrolled heart failure, recent heart attack or stroke, or prior blood clots.

Monitoring is part of treatment

TRT is a long-term commitment, not a one-time prescription. Standard care includes blood tests and check-ups several times in the first year and at least annually after that, tracking testosterone, hematocrit, and PSA as appropriate. Many side effects relate to doses that are too high, so regular lab review is how therapy stays safe and effective.

If you think you may have low testosterone, the right next step is a clinician and a blood test, not a self-diagnosis. Use our comparisons to find a provider that emphasizes testing and oversight.