What it is
A very long-acting esterified form of testosterone available as an injectable in castor oil (Aveed) or an oral softgel (Jatenzo).
How it works
The long aliphatic undecanoate ester slows hydrolysis, prolonging release. Oral undecanoate is absorbed via the intestinal lymphatic system, bypassing first-pass hepatic metabolism.
Where it's used
Used in hormone replacement therapy where extended dosing intervals are desired.
FDA-approved use
Replacement therapy in adult males for conditions associated with a deficiency or absence of endogenous testosterone.
Tracking it
Testosterone Undecanoate is injectable, so two things matter in a log: when you dosed and where. Rotating sites and writing both down prevents the classic “did I already pin the left side?” problem. with a half-life of about 21 days (504 h), a dose log also lets a tracker model the relative amount still in your system between doses.
Source
OpenFDA
Last reviewed 2026-06-11