What is TRT?

What the term covers

“TRT” denotes replacement of testosterone to a physiological range in men whose own production is deficient. The 2018 Endocrine Society clinical practice guideline frames it as treatment for hypogonadism — a condition defined by the combination of consistent signs or symptoms and unequivocally low serum testosterone, not by a number alone. The guideline states that diagnosis requires symptoms together with low morning total testosterone measured on at least two separate occasions, using an accurate assay.

That two-part definition is the reason the same measured value can carry different clinical meaning in two different men. It is also why the guideline separates replacement, which restores a deficient level, from supraphysiological administration, which does not — the latter is outside what the label and the guideline describe.

What counts as a low level

Reference ranges are assay-dependent, which historically made cross-laboratory comparison unreliable. Travison and colleagues (2017, Journal of Clinical Endocrinology & Metabolism) published harmonized normative ranges derived from four cohorts, reporting a normal total-testosterone range of 264–916 ng/dL in healthy nonobese men aged 19–39. Those figures are what the harmonized standard reports; individual laboratories continue to publish their own ranges.

The harmonized range, how it was derived, and why laboratory ranges differ from it are set out in what is a normal testosterone level.

The FDA-labeled formulations

Several testosterone esters carry FDA labels, and the labels differ from one another in route and interval rather than agreeing on a single schedule. Depo-Testosterone (testosterone cypionate) is labeled for intramuscular injection every two to four weeks. Xyosted (testosterone enanthate auto-injector) is labeled for once-weekly subcutaneous injection with dose titration against trough concentrations. Transdermal gels and solutions carry daily labels. The interval on a label reflects that product’s pharmacokinetics, not a general rule about testosterone.

• Testosterone cypionate (Depo-Testosterone) — intramuscular, labeled every two to four weeks.
• Testosterone enanthate — two labels exist: the classic intramuscular label states 50–400 mg every two to four weeks; the Xyosted auto-injector label states weekly subcutaneous administration.
• Transdermal gels and solutions — daily application, with label warnings about secondary transfer.

The two enanthate labels and how they diverge are compared in how often testosterone enanthate is injected.

The cypionate interval, and what the literature reports about peak-to-trough management, are covered in how often testosterone cypionate is injected.

Whether the subcutaneous route is label-supported is addressed in can testosterone be injected subcutaneously.

What the evidence reports about onset

Saad and colleagues (2011, European Journal of Endocrinology) reviewed the time course of testosterone therapy’s reported effects and described them as staggered rather than simultaneous: effects on sexual interest were reported within weeks, while changes in body composition and bone density were reported over months to years. The review reports observed timelines across studies; it does not establish what any individual will experience.

The onset intervals reported for each outcome are set out in how long TRT takes to work.

Monitoring, as the guideline describes it

The 2018 Endocrine Society guideline describes evaluating men on testosterone therapy at three to six months after initiation and annually thereafter, with testosterone concentration, hematocrit and prostate-specific antigen among the parameters assessed. The guideline also describes hematocrit thresholds at which it recommends clinicians act. These are the guideline’s stated intervals and parameters; the monitoring a given clinician orders is a clinical decision.

The guideline’s stated schedule and the specific parameters are listed in how often bloodwork is done on TRT.

Reported adverse effects and the cardiovascular question

Erythrocytosis — a rise in hematocrit — is among the most frequently reported effects in the label and guideline literature, which is why hematocrit appears in the monitoring parameters above. Suppression of endogenous production and of spermatogenesis is also documented, and the guideline addresses fertility explicitly when discussing men who wish to preserve it.

On cardiovascular safety, the TRAVERSE trial (Lincoff et al., 2023, New England Journal of Medicine) randomized 5,246 middle-aged and older men with hypogonadism and preexisting cardiovascular disease or elevated risk to transdermal testosterone or placebo, and reported testosterone to be noninferior to placebo for the incidence of major adverse cardiac events. The trial reported higher incidences of pulmonary embolism, acute kidney injury and atrial fibrillation in the testosterone group. That is what the trial found in that population; it is not a general safety statement.

The mechanism behind the most commonly asked cosmetic question, and what the evidence does and does not show, is examined in does TRT cause hair loss.

The limits of this page

• This is not medical advice. It reports what labels, guidelines and trials state; it does not tell anyone whether to seek or continue treatment.
• Testosterone is a Schedule III controlled substance in the United States and is dispensed by prescription. Prof. Peptide does not list vendors, codes or prices for it, and no part of this site sources it.
• A guideline is a recommendation to clinicians, not a rule binding one. Labels describe what a product was approved for, not the whole of documented practice.
• Reference ranges are assay-dependent, and a single measurement is not a diagnosis — the guideline requires repeated morning measurements alongside symptoms.

How Prof. Peptide sources and checks what it publishes is set out in the methodology.