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
| Class | Injectables |
|---|---|
| Half-life | 33.9 days castor oil IM (Nebido/Aveed); 20.9 days tea seed oil IM; 3-5 hours oral (dietary-fat-dependent) |
| Absorption half-life | 33.9 ± 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 window | 180 days |
| Aromatization | Yes |
| Hepatotoxicity | Low (injectable), Medium (oral) |
| Suppression | 10/10 |
| 17α-alkylated | No |
| Administration | injectable |
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 — pharmacokineticLetrozole 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 — synergisticGood 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
- Behre HM et al.. 2004. Testosterone: Action, Deficiency, Substitution — Half-life 20.9 days (tea seed oil) to 33.9 days (castor oil) IM
- de Oliveira Vilar Neto JF et al.. 2021. Andrologia — Systematic review: only 4/38 known-outcome AAS-induced hypogonadism cases fully recovered
- 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
- 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)
- 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)
- 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
- Bhasin S et al.. 2001. Am J Physiol Endocrinol Metab — Estradiol rise with supraphysiologic testosterone - class effect independent of ester; supports aromatizationRate 6/10
- Hartgens F, Kuipers H. 2004. Sports Medicine — Testosterone undecanoate (injectable) minimal hepatic impact; oral formulation absorbed via lymphatic route bypasses hepatic first-pass
- 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.