Testosterone enanthate

What it is

Testosterone enanthate is an injectable ester of testosterone used to treat men with confirmed hypogonadism due to structural or genetic causes. It's pharmacologically almost identical to testosterone cypionate, differing only in the length of its ester side chain, and it has one of the longest FDA approval histories of any testosterone product — dating back to 1953.¹

Also known as: Delatestryl (the branded intramuscular formulation) and Xyosted (a subcutaneous auto-injector version approved in 2018), plus multiple generic "Testosterone Enanthate Injection, USP" products.¹ Xyosted is worth calling out separately — it's the only enanthate product specifically approved for subcutaneous injection, and it carries its own distinct safety labeling discussed below.

Beyond hypogonadism, the Delatestryl label also covers delayed puberty in carefully selected boys and, less commonly today, palliation of inoperable metastatic breast cancer in postmenopausal women — indications that reflect the drug's decades-long history rather than current mainstream use.

How it works

Testosterone enanthate shares the identical receptor pharmacology of native testosterone once its ester is cleaved. The 17β-hydroxyl group is esterified with heptanoic (enanthic) acid — a 7-carbon side chain, one carbon shorter than cypionate's — which increases lipophilicity and slows release from an intramuscular or subcutaneous depot. Tissue and plasma esterases hydrolyze that ester in the body, freeing testosterone to act through its usual pathways: binding the androgen receptor directly, converting to the more potent dihydrotestosterone (DHT) in skin and prostate tissue, and aromatizing to estradiol in fat tissue.¹

Like all exogenous testosterone, enanthate suppresses the hypothalamic-pituitary-gonadal axis through negative feedback — rising testosterone and estradiol tell the brain to reduce LH and FSH output, which in turn suppresses the testes' own testosterone production and sperm output. This is the physiological basis for combining TRT with hCG or an alternative like enclomiphene when fertility preservation matters.

Because native testosterone's plasma half-life is only about 10 minutes, esterification is what makes enanthate usable as an injectable. Its 7-carbon chain gives it an effective half-life of roughly 7 days — marginally shorter than cypionate's ~8 days — with peak serum concentrations 24–72 hours after an intramuscular dose and steady state reached in about 4–5 weeks of consistent dosing.¹⁵ By weight, enanthate is about 72.0% testosterone versus 69.9% for cypionate — a difference small enough that the two are dosed roughly 1:1 by milligram in practice.

What the research shows

Animal / preclinical evidence

As with other testosterone esters, enanthate's receptor-level pharmacology has long been established in animal and cell models, but current clinical decisions rest on human trial data rather than preclinical work, since androgen biology is well characterized and the clinically relevant open questions (cardiovascular risk, fracture risk) require human outcome data.

Human evidence

The pivotal trial informing enanthate's current safety labeling is TRAVERSE, a randomized, placebo-controlled, FDA-mandated trial of 5,246 hypogonadal men with cardiovascular risk factors.⁵ Although it studied transdermal gel, its findings — noninferiority for major cardiac events (7.0% vs 7.3%, HR 0.96), alongside statistically significant increases in atrial fibrillation (3.5% vs 2.4%) and acute kidney injury (2.3% vs 1.5%) — directly triggered the 2024–2025 FDA label revisions applied to enanthate products, including removal of the cardiovascular boxed warning.¹³

Enanthate has its own product-specific safety data too: the Xyosted (subcutaneous auto-injector) approval program found that while the drug reliably normalized testosterone, ambulatory blood pressure monitoring revealed clinically meaningful blood pressure increases — enough that the FDA required a unique boxed warning for blood pressure and cardiovascular risk, the only testosterone product to carry that specific warning before the 2025 class-wide update.⁶

Broader class-wide evidence applies here as well. The Testosterone Trials (790 men over 65, using transdermal gel) found modest gains in sexual function and mood but no clear benefit for walking distance or vitality.⁷ A 2018 meta-analysis of four RCTs (N=1,779) found small improvements in libido and sexual satisfaction, no effect on energy or mood, and an eightfold increase in erythrocytosis versus placebo — a signal directly relevant to enanthate given its similar peak-trough pharmacokinetics to cypionate.⁸ The TRAVERSE bone fracture substudy, though conducted with gel, found a statistically significant increase in clinical fractures despite improved bone density — a class-wide finding equally relevant to enanthate given matched testosterone exposure targets.¹⁰ An earlier, smaller trial in frail older men was stopped early for excess cardiovascular events, a cautionary finding not replicated by the larger TRAVERSE trial.⁹

Honest bottom line: enanthate's efficacy and safety picture is, by design, borrowed from the broader testosterone evidence base rather than tested in its own dedicated outcomes trial — reasonable given the pharmacological logic, but worth knowing if you're weighing product-specific proof versus class-wide extrapolation. The one place enanthate has genuinely unique trial data is the Xyosted blood-pressure signal, which foreshadowed a warning later applied to the entire testosterone class.

Typical use and dosing

The Delatestryl (intramuscular) label specifies 50–400 mg every 2–4 weeks for replacement therapy, noting that injections more often than every 2 weeks are "rarely indicated" because of the ester's prolonged action.² The Xyosted subcutaneous auto-injector is labeled for a starting dose of 75 mg once weekly, titrated based on testosterone response.⁶ For the delayed-puberty indication, dosing is 50–200 mg every 2–4 weeks for a limited course, typically 4–6 months, with periodic bone-age imaging.

As with other testosterone esters, therapy for confirmed hypogonadism is generally long-term, with reassessment recommended at 3–6 months to confirm testosterone has normalized and symptoms have improved.¹⁴

Safety, side effects, and who should avoid it

Commonly reported side effects include injection-site reactions (bruising for the Xyosted auto-injector, pain/induration for intramuscular dosing), increased hematocrit, and headache. For Xyosted specifically, the most frequently reported adverse reactions (over 5%) were hematocrit increase, hypertension, PSA increase, injection-site bruising, and headache.⁶ Less common effects (roughly 1–10%) include gynecomastia, mood changes, elevated PSA, worsening of benign prostatic hyperplasia symptoms, and suppressed sperm production with prolonged use.

Rarer but serious risks include peliosis hepatis and hepatic neoplasms with prolonged high-dose use (more historically associated with oral androgens, but included in labeling), hypercalcemia in immobilized patients, and suppression of clotting factors that can increase bleeding risk in patients on anticoagulants. Drug interactions to flag: warfarin (potentiated anticoagulant effect), insulin/oral hypoglycemics (androgens can enhance insulin sensitivity), and, for Xyosted specifically, other blood-pressure-affecting medications given the drug's own hypertensive effect.

Monitoring follows the same general pattern as other testosterone products: baseline comprehensive morning fasting panel — total and free testosterone, LH, SHBG, hematocrit, PSA (for men over 40), lipids, and metabolic markers; repeat testosterone and hematocrit at 3–6 months; and ongoing testosterone checks every 6–12 months, with hematocrit checked roughly every 3 months for Xyosted per its label, or at 3–6 months then annually for standard intramuscular dosing.¹³ Blood pressure monitoring starting around 6 weeks after initiation is now part of the class-wide 2025 FDA labeling update.

Regulatory status

Delatestryl was originally approved in 1953, making it one of the oldest testosterone products still marketed; Xyosted, the subcutaneous auto-injector version, was approved in 2018.⁶ Both are DEA Schedule III controlled substances under the Anabolic Steroids Control Act.¹ Neither is approved for age-related hypogonadism — labeling explicitly limits use to structural or genetic causes, and this limitation is a formal contraindication (not just a "limitation of use") in the Xyosted label specifically.

In August 2024, the FDA published a Federal Register determination affirming Delatestryl was not withdrawn for safety or efficacy reasons, part of routine regulatory housekeeping for a drug with this long a market history.⁴ The February 2025 class-wide FDA labeling action — prompted by TRAVERSE and blood-pressure monitoring data — removed the cardiovascular boxed warning while adding blood-pressure warnings across the entire testosterone product class, building on the precedent Xyosted's own label had already set.¹³ As a small-molecule steroid, testosterone enanthate remains eligible for 503A/503B compounding, unlike hCG.

Frequently asked questions