TRT: What Is Testosterone Replacement Therapy?

Men's Lifestyle, Testosterone Therapy

Testosterone replacement therapy (TRT) is a medical treatment for men whose bodies do not produce adequate testosterone. It is one of the more widely discussed and sometimes misunderstood treatments in men’s health. For men with confirmed hypogonadism, TRT can meaningfully improve quality of life, body composition, energy, mood, and sexual function. For men without true deficiency, it carries risks without proportional benefits. Understanding what TRT is, how it works, and who it is appropriate for is essential before making any treatment decisions. For context on the condition it treats, see our overview of what low testosterone is and how it is diagnosed.

What Is TRT and How Does It Work?

TRT works by supplying exogenous (externally administered) testosterone to the body. This supplements or replaces the testosterone the testes would normally produce. The administered testosterone enters the bloodstream, binds to androgen receptors in target tissues throughout the body, and produces the same biological effects as endogenous testosterone: supporting muscle, bone, brain, cardiovascular, and sexual function ( 1 ).

One important consequence of exogenous testosterone is suppression of the body’s own production. When the brain’s hypothalamus and pituitary detect adequate testosterone in the blood, they reduce the signals (GnRH, LH, FSH) that would normally stimulate testicular testosterone production. This is a normal physiological feedback response. It means that TRT, while restoring testosterone levels, reduces or eliminates the testes’ own output and can affect sperm production, which is a relevant consideration for men who wish to preserve fertility.

Who Is TRT For?

TRT is indicated for men with clinically confirmed hypogonadism: consistently low testosterone levels (typically below 300 ng/dL on two morning tests) combined with symptoms of deficiency. It is not indicated for men with low-normal testosterone who are asymptomatic, nor as a general anti-aging or performance-enhancing intervention in men with normal levels ( 1 ).

Candidates for TRT undergo a thorough evaluation that includes lab work (total and free testosterone, LH, FSH, prolactin, hematocrit, PSA, and metabolic markers), a review of symptoms, a discussion of health history and medications, and in some cases imaging if a pituitary abnormality is suspected. The goal is to confirm true hypogonadism, identify the cause, and ensure no contraindications exist before starting therapy.

Delivery Methods for TRT

TRT is available in several forms, each with distinct pharmacokinetic profiles, administration schedules, and practical considerations:

Intramuscular Injections

Testosterone cypionate and testosterone enanthate are the most commonly used injectable forms in the United States. They are administered via intramuscular or subcutaneous injection, typically once or twice per week, into the gluteal muscle or the subcutaneous tissue of the abdomen or thigh. Injections produce a peak in testosterone shortly after administration, followed by a gradual decline over the dosing interval. More frequent, lower-dose injections produce more stable levels than less frequent, higher-dose injections ( 2 ).

Topical Gels and Creams

Transdermal testosterone gels applied daily to the skin provide relatively stable testosterone levels and avoid the peaks and troughs associated with injections. The main practical concern is transfer risk: testosterone can transfer to partners or children through skin contact if the application site is not covered or washed thoroughly. Gels are absorbed variably across individuals, which can affect dosing predictability.

Transdermal Patches

Testosterone patches applied to the skin deliver testosterone continuously over 24 hours. They have a lower transfer risk than gels but are associated with higher rates of skin irritation at the application site. Patches are less commonly used today compared to injections and gels.

Testosterone Pellets

Pellets are small, rice-sized implants inserted under the skin (typically in the buttock) during a brief in-office procedure. They release testosterone gradually over three to six months and do not require daily or weekly administration. Pellet therapy provides highly stable levels but cannot be easily adjusted or removed if side effects occur.

Oral and Nasal Formulations

Oral testosterone undecanoate and intranasal testosterone gel are newer formulations. The oral form requires administration with food and avoids first-pass liver metabolism through a lymphatic absorption mechanism. The nasal gel is applied directly to the nostrils and provides a short duration of action requiring multiple daily doses. Both formulations offer options for men who prefer to avoid injections or topical skin preparations.

What TRT Can and Cannot Do

For men with genuine hypogonadism, TRT reliably raises testosterone levels. Clinical benefits that are well-documented include improvements in libido, sexual function, mood, energy, lean body mass, and bone mineral density ( 1 ), ( 3 ). These effects develop over different time horizons: libido and mood often improve within weeks; body composition changes typically require several months of consistent therapy.

TRT does not reliably restore fertility. Because it suppresses the HPG axis and reduces FSH, sperm production typically declines on TRT. Men who want to maintain fertility have alternative options, including clomiphene citrate or human chorionic gonadotropin (hCG), which stimulate the body’s own testosterone production without suppressing sperm output. For a detailed discussion, see our article on TRT and fertility.

Common Myths About TRT

A common myth is that TRT is essentially the same as anabolic steroid abuse. This conflates therapeutic use, aimed at restoring physiological testosterone levels in deficient men, with supraphysiological doses used without medical indication. They are different in purpose, dosing, monitoring, and risk profile.

Another myth is that TRT causes prostate cancer. This concern originated from older, outdated research. Major guidelines from the American Urological Association and the Endocrine Society do not support the idea that TRT at physiological levels causes prostate cancer. However, it is contraindicated in men with known or suspected prostate cancer, and ongoing PSA monitoring is standard during treatment ( 2 ).

When to See a Provider

TRT is a prescription medical treatment and should only be initiated after a thorough clinical evaluation. Self-medicating with testosterone purchased outside of medical channels carries significant health risks, including cardiovascular complications, polycythemia, and infertility, without appropriate monitoring.

If you are experiencing symptoms consistent with low testosterone, speaking with a men’s health provider is the right first step. A proper diagnosis and individualized treatment plan will determine whether TRT is appropriate for your specific situation.

Emergency Notice: If you or someone else is experiencing a medical emergency, call 911 immediately. The information on this site is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.