What Is Testosterone Replacement Therapy (TRT)? A Complete Guide for Men

Testosterone replacement therapy — commonly referred to as TRT — has become one of the most discussed treatments in men's health. Use has increased significantly over the past two decades, driven in part by greater awareness of low testosterone, broader access through telehealth, and a growing body of clinical research on its effects. Despite the increased visibility, there is still considerable confusion about what TRT actually is, who it is appropriate for, what it can and cannot do, and what risks it carries. This article provides a straightforward, evidence-based overview of TRT for men who want to understand the treatment before making decisions about their health.

What Is TRT?

Testosterone replacement therapy is a medical treatment that uses externally administered testosterone to restore blood testosterone levels to within the normal physiological range in men who have clinically confirmed testosterone deficiency. The goal is not to push testosterone above normal limits but to bring levels back to where they would be in a healthy, functioning male — generally between 300 and 1,000 ng/dL, with most providers targeting the mid-normal range.

TRT is prescribed for men with hypogonadism, a condition in which the testes do not produce adequate testosterone. It is not intended — and should not be used — as a performance-enhancing therapy in men whose testosterone levels are already normal. The distinction between medically supervised TRT at physiological doses and the supraphysiological use of testosterone seen in anabolic steroid abuse is significant: the former is FDA-approved and clinically appropriate; the latter carries serious health risks and is not medically sanctioned.

Who Is TRT For?

TRT is indicated for men with a diagnosis of testosterone deficiency, which requires both of the following: a total serum testosterone level below 300 ng/dL measured on two separate morning blood draws, and symptoms consistent with hypogonadism. Symptoms that may indicate low testosterone include decreased libido, erectile dysfunction, persistent fatigue, loss of muscle mass, increased body fat, depressed mood, and reduced concentration.

The American Urological Association recommends that TRT not be initiated based on lab values alone or symptoms alone — both must be present. A thorough clinical evaluation should be conducted before starting treatment, including assessment of the cause of hypogonadism (primary versus secondary), review of other conditions that may mimic low testosterone, and discussion of the patient's goals and concerns regarding fertility.

Types of TRT

Multiple formulations of testosterone are available by prescription. Each has a different delivery mechanism, dosing schedule, and set of practical considerations. A healthcare provider will recommend the most appropriate form based on the patient's clinical profile, lifestyle, and preferences.

Testosterone Injections

Intramuscular or subcutaneous injections of testosterone esters — most commonly testosterone cypionate or testosterone enanthate — are among the most widely used and cost-effective forms of TRT. They are typically administered every one to two weeks, though some providers prescribe smaller weekly doses to minimize peaks and troughs in hormone levels. Injections produce reliable increases in serum testosterone and are straightforward to monitor. The main drawbacks are that they require either self-injection or clinical administration, and that testosterone levels fluctuate between doses, which some men find affects mood and energy.

Topical Gels and Creams

Testosterone gels and creams are applied daily to the skin — typically on the upper arms, shoulders, or inner thighs — where the hormone is absorbed transdermally into the bloodstream. They provide steadier testosterone levels than injections and are convenient for daily use. The primary concern with topical formulations is the risk of unintentional transfer to partners or children through skin contact, which can cause hormonal changes in those who are exposed. Proper hygiene protocols — washing hands after application and covering the application site — are essential.

Testosterone Patches

Testosterone patches are applied daily to the skin and deliver a controlled dose of testosterone through slow transdermal absorption. They are less widely used than gels due to a higher incidence of skin irritation at the application site, but they remain an option for men who prefer a patch-based format.

Oral Testosterone

Oral testosterone undecanoate (sold under the brand name Jatenzo in the US) is an FDA-approved oral formulation that is taken twice daily with food. It avoids first-pass liver metabolism due to its lymphatic absorption pathway. Certain oral testosterone formulations may be less suppressive of endogenous testosterone production than injectable forms, and LH and FSH — markers of fertility — remain within normal range in a meaningful proportion of users. Oral TRT is taken with a high-fat meal to optimize absorption.

Testosterone Pellets

Pellets containing crystalline testosterone are implanted subcutaneously (under the skin, typically in the buttocks or hip area) by a physician and release testosterone gradually over three to six months. The primary advantage is convenience — once implanted, no daily dosing is required. The primary disadvantage is that the dose cannot be easily adjusted once pellets are placed, and if side effects arise, the dose cannot be reduced immediately.

Nasal Testosterone Gel

A nasal testosterone gel (brand name Natesto) is applied to each nostril three times daily. It delivers testosterone through the nasal mucosa. This formulation has a shorter half-life and may have less suppressive effect on sperm production than other forms of TRT, making it a consideration for men who want to treat low testosterone while minimizing fertility impact.

What Results Can Men Expect From TRT?

TRT does not produce overnight changes. Effects unfold over a variable timeline depending on the symptom being addressed. The Testosterone Trials — a set of coordinated clinical trials involving over 700 men aged 65 and older with confirmed low testosterone — provide some of the most rigorous data available on TRT outcomes.

Sexual function: Improvements in sexual desire typically begin within three to eight weeks of treatment. Improvements in erections and ejaculatory function tend to follow over two to three months, with peak effects occurring several months into sustained treatment.

Energy and mood: Many men report improvements in energy, motivation, and mood within the first few weeks, though the extent and consistency of these changes vary. TRT has been shown to improve depressive symptoms in hypogonadal men, though it is not a treatment for clinical depression in men with normal testosterone levels.

Body composition: Changes to lean muscle mass and fat distribution typically take longer — most studies show meaningful changes in body composition at six to twelve months of consistent treatment. TRT increases muscle protein synthesis and is associated with reductions in fat mass, particularly visceral fat.

Bone density: Testosterone has a protective effect on bone mineral density. Improvements in bone density with TRT tend to develop slowly and are typically measurable at twelve to twenty-four months.

Risks and Side Effects of TRT

TRT is generally well tolerated when properly prescribed and monitored, but it carries a number of documented risks that men should understand before starting treatment.

Fertility suppression: All forms of TRT suppress the body's natural production of testosterone by suppressing the hypothalamic-pituitary-gonadal axis — specifically, by reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which signal the testes to produce testosterone and sperm. This results in a reduction in sperm production that can lead to infertility during treatment. Men who wish to conceive should discuss this risk with their provider before starting TRT and consider alternative approaches.

Erythrocytosis: TRT stimulates red blood cell production. This can elevate hematocrit above normal ranges, increasing blood viscosity and the theoretical risk of thrombotic events. Routine monitoring of hematocrit is a standard part of TRT management, and dose adjustments or therapeutic phlebotomy may be needed if levels rise too high.

Testicular atrophy: Because TRT suppresses LH, which normally stimulates testosterone production in the testes, testicular volume tends to decrease during treatment.

Acne and oily skin: Androgens stimulate sebaceous gland activity. Some men on TRT experience increased acne, particularly during initial dose adjustments.

Cardiovascular considerations: The cardiovascular effects of TRT have been the subject of ongoing research and debate. Earlier concerns were raised by a 2010 trial, which was halted due to a higher rate of cardiovascular events in the TRT group. Subsequent, larger studies — including the TRAVERSE trial — found no significant increase in major adverse cardiovascular events in men on TRT compared to placebo, though some increased risk of nonfatal arrhythmias and pulmonary embolism was observed. Men with existing cardiovascular disease should have a thorough discussion with their physician before starting TRT.

Sleep apnea: TRT can worsen sleep apnea in men who already have the condition. Men with untreated severe sleep apnea are generally not candidates for TRT until the apnea is managed.

Who Should Not Use TRT?

TRT is contraindicated or requires additional caution in men with the following conditions: active or suspected prostate cancer, breast cancer, untreated severe sleep apnea, elevated hematocrit (above approximately 54%), uncontrolled heart failure, and recent history of stroke or heart attack. Men who wish to father children in the near future should also carefully weigh the fertility implications and discuss alternatives before starting therapy.

Monitoring on TRT

TRT requires ongoing clinical monitoring. Standard monitoring typically includes: testosterone levels (to confirm levels are in the target range and avoid supraphysiological elevations), hematocrit (to screen for erythrocytosis), prostate-specific antigen (PSA) and digital rectal exam (in men over 40, to screen for prostate disease), and lipid panel. The frequency of monitoring varies by provider but is generally most intensive in the first year of treatment.

Alternatives to TRT

For men who want to raise testosterone levels without the fertility and suppression-related side effects of TRT, several alternatives exist. Clomiphene citrate (FDA-approved for ovulation induction in women, used off-label in men) and enclomiphene citrate (not FDA-approved) are selective estrogen receptor modulators that block estrogen receptors in the hypothalamus, prompting the body to increase production of LH and FSH and thereby stimulate natural testosterone production. Because these approaches work with the body's own hormone axis rather than replacing it externally, they do not suppress sperm production and are considered fertility-preserving options.

Human chorionic gonadotropin (hCG) mimics LH and can be used to stimulate testicular testosterone production. It is sometimes used in combination with TRT to preserve testicular function and fertility, or as an alternative in men with secondary hypogonadism.