Testosterone Undecanoate (oral, Andriol)
Oral testosterone ester (undecanoate) formulated in oleic acid to be absorbed via the intestinal lymphatics, bypassing first-pass hepatic metabolism. Marketed as Andriol/Restandol for testosterone replacement, it avoids the 17-alpha-alkylation hepatotoxicity of older oral androgens but delivers erratic, food-dependent, short-lived serum levels.
01 Overview
Testosterone undecanoate is testosterone esterified at the 17-beta position with a long undecanoic acid chain. When taken orally in an oil-filled capsule with a fatty meal, a fraction is absorbed through intestinal lymphatic vessels rather than the portal vein, escaping the extensive first-pass liver metabolism that renders plain oral testosterone useless. Because it is not 17-alpha-alkylated it carries little hepatotoxic burden, distinguishing it from methyltestosterone and other classic oral steroids.
The practical drawback is pharmacokinetics: absorption is heavily dependent on dietary fat, serum testosterone peaks a few hours after dosing and falls quickly, requiring 2-4 doses per day, and levels vary widely between individuals. It has been used clinically for hypogonadism and delayed puberty for decades in Europe and elsewhere; a newer US reformulation (Jatenzo) uses the same lymphatic strategy. Recreational use for muscle gain is limited by cost and unreliable blood levels.
02 Mechanism
After lymphatic absorption the undecanoate ester is cleaved to release free testosterone, which acts as a full agonist at the androgen receptor and can aromatise to estradiol and be 5-alpha-reduced to DHT, driving the normal spectrum of androgenic and anabolic effects.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| TRT | 120–240 mg/day | Oral | Divided doses taken with fatty meals; titrated to serum levels. |
| Supraphysiologic (anecdotal) | 240–400 mg/day | Oral | Recreational; blood levels unreliable and cost high. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Restored serum testosteroneCorrects hypogonadal symptoms when dosed with fatty food; levels fluctuate through the day. | into mid-normal range | Clinical | |
| Lean mass and libido improvementDocumented in TRT trials, comparable to other testosterone forms at equivalent exposure. | Clinical | ||
| Low hepatic burdenNot 17-alpha-alkylated, so liver enzyme elevation is minimal compared with classic oral steroids. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Erratic, food-dependent blood levelsAbsorption swings widely with dietary fat and between individuals, complicating dosing. | Mild | Inherent to formulation | Clinical | |
| HPTA suppressionExogenous testosterone suppresses LH/FSH and endogenous production. | Moderate | Universal at supraphysiologic doses | Clinical | |
| Estrogenic effectsGynecomastia and water retention from aromatisation to estradiol. | Mild | Dose-dependent | Clinical |