This information is for research and educational purposes only. No medical recommendations. Products are not approved for human use. For health questions, consult a doctor.

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Muscle & performance

Testosterone Undecanoate

The ultra-long testosterone ester - very infrequent injections, classic in TRT.

1 min read 2 sources Titration Updated June 2026

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Class: Testosterone ester (ultra-long)
Use: Intramuscular (subQ possible), very infrequent
Half-life: very long (weeks)
WADA: banned (anabolic)

Getting started

Typical dosing (research context)

Per-week figures in mg. Very long ester - in TRT often only every few weeks, in building rather weekly.

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What is Testosterone Undecanoate?

Testosterone Undecanoate is testosterone with the ultra-long undecanoate ester. In clinical TRT (brand name Nebido) it is injected only every few weeks - the compound is released extremely slowly. That gives very stable levels without frequent injecting.

This information is for research and educational purposes only. No medical advice.

How it works

Like all testosterone esters: androgen receptor activation, protein synthesis, nitrogen retention, partial aromatization to estradiol. The only difference is the very slow release due to the long ester.

Use and dosing

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What the research shows

Testosterone research (Bhasin et al., NEJM 1996) applies to all esters equally. Testosterone undecanoate is clinically established as a TRT preparation; AAS pharmacology: Kicman 2008.

Side effects

Estrogen-related: water retention, gyno risk with high aromatization.
Possible hematocrit rise.
HPTA suppression - PCT topic.
Androgenic: acne, hair loss in predisposed individuals.

Storage

Store the oil solution at room temperature, protected from light - no fridge needed. Out of reach of children.

Practice

PCT / after coming off

Anabolic substances suppress the body's own testosterone production in the research context. Anyone who comes off a cycle (rather than running it continuously) typically uses a post-cycle therapy (PCT) to restart the natural axis (HPTA).

The standard scheme in the research/literature context combines a SERM (tamoxifen and/or clomifene, alternatively enclomiphene) over roughly four weeks, optionally preceded by HCG to re-sensitise the testes before the SERM block. An aromatase inhibitor (anastrozole/exemestane) belongs more to on-cycle estrogen control than to the PCT itself.

Tip: order the PCT items together with the cycle so they are already on hand when you come off.

This information serves research and educational purposes only. Not medical advice.

Tamoxifen (Nolvadex) SERM, core of PCT Clomid (Clomifen) SERM, core of PCT Enclomiphene (Androxal) SERM alternative HCG testicular restart before PCT Arimidex (Anastrozole) aromatase inhibitor, on-cycle Aromasin (Exemestane) aromatase inhibitor, on-cycle

Evidence

Sources

1 Supraphysiologic testosterone doses increase muscle size and strength in healthy men. Bhasin et al., NEJM, 1996
2 Pharmacology of anabolic steroids - comprehensive review. Kicman, Br J Pharmacol, 2008

Keep reading

More in the lexicon

Test Base (Testosterone Suspension) - Research Substance Aqueous suspension of pure testosterone without ester for rapid absorption in research contexts. Read Test Suspension Ester-free testosterone in water - immediate effect, short, often used pre-workout. Read Testosterone Enanthate The long testosterone ester - the standard base of almost every research protocol. Read

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Testosterone Undecanoate in the catalog

Sizes, prices and availability for research use. Straight from the lexicon to the product page.

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