Testosterone Undecanoate Profile

Half-life: 20 to 34 days (castor oil depot absorption)
Peak concentration (Tmax): approximately 4 days post-injection
Steady state: achieved after the loading phase (Day 1, Week 4, then every 10 to 14 weeks)
Volume: 3 to 4 mL of oily solution administered as a single deep gluteal injection
Key advantage: lowest injection frequency of any testosterone ester (6 to 7 injections per year)

Half-life: 1.6 hours (terminal elimination)
Absorption: via intestinal lymphatic system, requires dietary fat co-administration (Jatenzo) or phytosterol excipient (Kyzatrex)
Dosing: twice daily to maintain eugonadal levels
Titration range: 158 mg to 237 mg per dose
Key advantage: no injection, no POME risk, potential absence of erythrocytosis

Frequently Asked Questions

What is testosterone undecanoate?

Testosterone undecanoate (TU) is a long-chain ester of testosterone available in both injectable (Aveed, Nebido) and oral (Jatenzo, Kyzatrex, Tlando) formulations. It is used for testosterone replacement therapy in men with confirmed hypogonadism.

How does oral testosterone undecanoate avoid liver damage?

Oral TU is absorbed through the intestinal lymphatic system rather than the portal vein, bypassing first-pass hepatic metabolism entirely. This eliminates the cholestasis and liver enzyme elevation caused by older 17-alpha-alkylated oral steroids like methyltestosterone.

What is POME and how common is it with Aveed injections?

Pulmonary Oil Microembolism (POME) occurs when oil droplets from the castor oil depot enter the lungs, causing coughing, chest pain, and difficulty breathing. It occurs in approximately 0.1% of injections and requires a mandatory 30-minute post-injection observation period under a REMS program.

What did the TRAVERSE trial prove about TRT and heart safety?

The TRAVERSE trial (5,246 men, 33-month median follow-up) showed that TRT was non-inferior to placebo for major adverse cardiovascular events (MACE). However, it identified higher rates of atrial fibrillation (3.5% vs 2.4%), pulmonary embolism, and acute kidney injury in the TRT arm.

How often do you need to inject testosterone undecanoate?

Injectable TU (Aveed) follows a loading protocol of Day 1, Week 4, then every 10 weeks. Nebido is typically administered every 10 to 14 weeks. This means approximately 6 to 7 injections per year, the lowest frequency of any testosterone ester.

Is Kyzatrex really zero percent erythrocytosis?

Kyzatrex clinical trials reported a 0% rate of erythrocytosis, compared to 1.3% for injectable Aveed and up to 23% in some TRT retrospective studies. The proposed mechanism is that oral delivery avoids the supraphysiological spike that overstimulates red blood cell production. This is a single-trial finding that requires confirmation in larger populations.

Can peptides replace testosterone undecanoate?

Peptides like Kisspeptin-10 can stimulate endogenous testosterone production without HPG axis suppression, while Tesamorelin targets visceral fat directly. However, no multi-arm RCTs compare peptides head-to-head with TU, and peptides cannot match the direct androgenic effect of exogenous testosterone for severe hypogonadism.

Does testosterone undecanoate affect fertility?

Yes. TU suppresses the HPG axis at therapeutic doses, leading to testicular atrophy and azoospermia typically within 4 to 6 months. Sperm recovery after cessation usually takes 6 to 24 months but is not guaranteed. Fertility preservation planning is essential before starting therapy.

TRT+: Testosterone Undecanoate

1.The Dual-Formulation Ester

2.Lymphatic Absorption: Bypassing the Liver

Explore This Profile

Safety Triggers

Research Gaps

Contrarian Views

Common Usage Patterns

Related Research

The Age Equation: When TRT Risk Changes and What the Alternatives Look Like

Testosterone Cypionate

Testosterone Enanthate

Testosterone Propionate

Muscle Growth: Hypertrophy

Fat Loss: Lipolysis

Stay Ahead of the Research

3.TRAVERSE Trial: Cardiovascular Safety Data

4.POME: The Injectable-Specific Risk

5.The 0% Erythrocytosis Claim

6.Dual Formulation Pharmacokinetics

7.Age-Stratified Risk Assessment

8.Peptide Alternatives

9.Bottom Line

The Verdict