Trenbolone Undecanoate
A very long-ester form of trenbolone using the undecanoate ester, giving the slowest release of the common trenbolone preparations. It offers the same extremely potent, non-aromatising trenbolone activity with far less frequent injection, at the cost of a very long time to clear and delayed offset of side effects. It has no clinical history and only anecdotal human data.
01 Overview
Trenbolone undecanoate esterifies trenbolone with undecanoic acid, an eleven-carbon chain producing a slow, prolonged release. It is the least common of the trenbolone esters, used to reduce injection frequency while retaining trenbolone's potent androgenic and anabolic properties.
As trenbolone, it does not aromatise but is strongly progestogenic and suppressive, and carries the characteristic neuropsychiatric and cardiovascular complaints (aggression, insomnia, night sweats, poor endurance). The long ester means that any side effects, once they appear, take a long time to subside, which is a notable practical drawback versus the acetate. There are no human clinical data.
02 Mechanism
High-affinity androgen-receptor agonist driving strong protein synthesis and nutrient partitioning; non-aromatising but progestogenic, with a very slow-release undecanoate ester.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Common | 200–300 mg/wk | IM | Long ester; less frequent injections than acetate. |
| Heavy | 400–500 mg/wk | IM | Side effects persist long after cessation. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Strength and lean mass gainPronounced strength and recomposition reported for trenbolone; no human trial data. | Anecdotal | ||
| No oestrogenic water retentionDoes not aromatise, giving a dry look; progestogenic gynaecomastia still possible. | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Neuropsychiatric effectsIrritability, insomnia and night sweats consistently reported with trenbolone; slower to resolve given the long ester. | Moderate | Common | Anecdotal | |
| Progestogenic gynaecomastia / sexual dysfunctionLibido loss and gynaecomastia via progesterone and prolactin pathways despite no aromatisation. | Moderate | Common | Anecdotal | |
| HPTA suppression (prolonged)Strong, prolonged suppression owing to potency and long ester. | Severe | Universal | Observational |