What undecanoate is
Undecanoate is the longest testosterone ester in circulation and the one where the carrier oil changes the answer. In castor oil with benzyl benzoate the release extends far beyond what the chain length alone would predict, which is the basis of long-interval clinical preparations.
- Ester chain
- 11-carbon (undecanoic acid)
- Half-life
- Approximately 20 to 34 days depending on the carrier oil.
- Testosterone fraction
- 61% by weight
- Per 100 mg of ester
- 61 mg of testosterone
- Presentation
- Oil solution, frequently in castor oil rather than a seed oil.
- Storage
- Room temperature, protected from light.
Weight, and why it is not a detail
Because the vehicle matters as much as the ester, published half-lives for undecanoate vary more widely than for any other testosterone ester. It carries the lowest testosterone fraction of the common esters at roughly 61%, so the gap between labelled milligrams and delivered hormone is at its widest here.
Where you meet it
Undecanoate is the outlier of the group, because the carrier oil changes the answer as much as the chain does. In castor oil with benzyl benzoate the release extends far beyond what an eleven-carbon chain alone would predict, which is the basis of long-interval clinical preparations and the reason published half-lives for it disagree so widely.
Nearest esters
The closest reference points on the release curve.
- Quanta Testosterone Undecanoate (TRT Choice)out of stock£30
Availability checked 2026-09-01. The product page carries live stock.
Common questions
Why do sources disagree on the undecanoate half-life?
Because the vehicle matters as much as the ester. Figures between roughly 20 and 34 days are all defensible depending on whether the preparation is in a seed oil or in castor oil.
Does undecanoate deliver less testosterone?
Per milligram of ester, yes. At about 61% it has the lowest testosterone fraction of the common esters, so the gap between labelled milligrams and delivered hormone is widest here.
How much testosterone is in Testosterone Undecanoate?
About 61% by weight. 100 mg of testosterone undecanoate contains roughly 61 mg of testosterone, the remainder being the ester chain.
Does this page give dosing information for Testosterone Undecanoate?
No. This is a reference resource covering the ester, its release profile, its weight and its storage. It does not provide dosing protocols, administration schedules or medical advice.