Testosterone Undecanoate — Dosing, Cycles, Half-Life & Side Effects

Testosterone Undecanoate is an injectable anabolic-androgenic steroid with a half-life of 33.9 days castor oil IM (Nebido/Aveed); 20.9 days tea seed oil IM; 3-5 hours oral (dietary-fat-dependent). Very long-acting testosterone ester requiring infrequent dosing. Complete HPTA shutdown with extended clearance time. Primary risks include strong HPTA suppression. This page is educational harm-reduction reference compiled from peer-reviewed literature — not medical advice, not an endorsement, not a recommendation to use. Consult a licensed clinician before any decision.

Quick Facts

ClassInjectables
Half-life33.9 days castor oil IM (Nebido/Aveed); 20.9 days tea seed oil IM; 3-5 hours oral (dietary-fat-dependent)
Absorption half-life33.9 ± 4.9 days castor oil depot (Behre HM et al. 1999); 20.9 days tea seed oil depot (Behre HM et al. 2004); oral lymphatic absorption (Bagchus WM et al. 2005 PMID 15713722)
Elimination half-life (free hormone)Free testosterone ~4-5 days after de-esterification (class effect); oral 3-5h (dietary-fat-dependent absorption-rate-limited)
Detection window180 days
AromatizationYes
HepatotoxicityLow (injectable), Medium (oral)
Suppression10/10
17α-alkylatedNo
Administrationinjectable

Typical Dosing Ranges

Common dose range: 750-1000mg every 10-12 weeks (TRT), 250-500mg/week (performance)

Cycle length: 12-20 weeks

Time to steady state: ~170 days

Dose ranges are compiled from published pharmacokinetic studies and community-reported usage. Where a value is community-reported rather than clinically studied, this page and its structured data flag it. Lower end of any range is always the safer starting point.

Stacking Considerations

  • No structural stacking blockers. Standard harm-reduction rules apply: minimize total androgen load, minimize oral exposure, and monitor bloodwork.

PCT Requirements

  • This compound causes clinically meaningful HPTA suppression. Post-cycle therapy is recommended.
  • Depot clearance estimate: ~170 days post-last-dose before SERM start (5 × apparent depot half-life of 814h).
  • Never stack two SERMs. Extend a single SERM (tamoxifen OR enclomiphene/clomiphene) rather than combining.
  • Use the cycle planner to generate a full protocol based on your complete stack, not this compound alone.

Side Effect Profile

  • Slow to clear
  • Requires loading dose
  • Limited availability
  • Expensive

Known Interactions

  • Testosterone Cypionate + Letrozole

    minor — pharmacokinetic

    Letrozole is potent AI. Over-suppression of estrogen is possible.

    Recommendation: Start with very low doses. Monitor E2 closely to avoid crash.

    Monitor: Estradiol, Joint pain, Mood

  • Testosterone Cypionate + Primobolan (Methenolone Enanthate)

    minor — synergistic

    Good synergy with low sides. Common stack.

    Recommendation: Generally well-tolerated combination.

    Monitor: Standard bloodwork

Related compounds

Monitoring (Bloodwork & Vitals)

  • Comprehensive metabolic panel (baseline, mid-cycle, post-cycle)
  • Lipid panel (total cholesterol, HDL, LDL, triglycerides)
  • CBC (hemoglobin, hematocrit — watch for erythrocytosis)
  • Sex-hormone panel (Total T, Free T, Estradiol sensitive, SHBG, LH, FSH)
  • Blood pressure (weekly self-check; flag systolic >140 or diastolic >90)

Baseline bloodwork is recommended before any cycle. Discontinue if liver enzymes exceed 3× upper limit of normal or if hematocrit exceeds 54%.

Frequently Asked Questions

What is the half-life of Testosterone Undecanoate?

Testosterone Undecanoate has a half-life of approximately 33.9 days castor oil IM (Nebido/Aveed); 20.9 days tea seed oil IM; 3-5 hours oral (dietary-fat-dependent). Clearance estimate: 814h × 5 = 4070h ≈ 170 days (castor oil Nebido/Aveed apparent terminal t½ 33.9 days; Behre HM et al. 1999 PMID 10523012). This figure is used to determine injection frequency (for esters) and post-cycle clearance timing.

What is the typical dose range for Testosterone Undecanoate?

Commonly reported ranges for Testosterone Undecanoate: 750-1000mg every 10-12 weeks (TRT), 250-500mg/week (performance). Cycle length: 12-20 weeks. These are compiled from published studies and community-reported usage — individual response varies and lower end is always preferred.

Does Testosterone Undecanoate suppress natural testosterone?

Testosterone Undecanoate causes severe suppression of the HPTA axis (score 10/10). Post-cycle therapy (PCT) is recommended after use.

Is Testosterone Undecanoate liver toxic?

Hepatotoxicity rating: Low (injectable), Medium (oral). Non-17αα compound — liver stress is lower but still warrants periodic monitoring during a cycle.

Does Testosterone Undecanoate aromatize to estrogen?

Aromatization profile: Yes. An aromatase inhibitor may be warranted if estrogen-related side effects appear — but AI use should be symptom-driven, not prophylactic, to avoid crashing E2.

What is Testosterone Undecanoate typically used for?

Testosterone Undecanoate is commonly used for: TRT, Long cycles, Cruise dose. Intended-use context does not imply safety — every use case carries the same underlying pharmacological risks.

Citations

  1. Behre HM et al.. 2004. Testosterone: Action, Deficiency, Substitution — Half-life 20.9 days (tea seed oil) to 33.9 days (castor oil) IM
  2. de Oliveira Vilar Neto JF et al.. 2021. Andrologia — Systematic review: only 4/38 known-outcome AAS-induced hypogonadism cases fully recovered
  3. Shankara-Narayana N et al.. 2021. J Endocrine Society — LH/FSH recovery approximately 52 weeks after 2 years testosterone undecanoate treatment; direct study on this compound
  4. Liu et al.. 2025. Substance Use & Misuse — AAS meta-analysis: SBP +12.43 mmHg (95% CI: 9.59-15.26), LDL-C +9.12 mg/dL (95% CI: 6.75-11.49)
  5. Behre HM / Bagchus WM et al.. 2005. Eur J Endocrinol — Testosterone undecanoate oral/IM PK - terminal half-life 33.9 days for IM injection, 5.8 hours for oral (dietary fat-dependent)
  6. Handelsman DJ / Shankara-Narayana N et al.. 2022. Eur J Endocrinol — LH/FSH recovery median 52 weeks after 2 years of TU - supports suppressionScore 10/10 with extended recovery timeline
  7. Bhasin S et al.. 2001. Am J Physiol Endocrinol Metab — Estradiol rise with supraphysiologic testosterone - class effect independent of ester; supports aromatizationRate 6/10
  8. Hartgens F, Kuipers H. 2004. Sports Medicine — Testosterone undecanoate (injectable) minimal hepatic impact; oral formulation absorbed via lymphatic route bypasses hepatic first-pass
  9. Schubert M, et al. Intramuscular testosterone undecanoate: pharmacokinetic aspects of a novel testosterone formulation. J Clin Endocrinol Metab. 2004;89(11):5429-34. PMID: 15531493

Disclaimer

StackItSmart is an independent harm-reduction reference. The content above is compiled from peer-reviewed literature and is not medical advice, not an endorsement, and not a recommendation to use Testosterone Undecanoate. Performance-enhancing compounds carry legal, endocrine, cardiovascular, and hepatic risks. Consult a licensed clinician before any decision. StackItSmart does not provide sourcing, procurement, or dosing prescriptions.

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