Penmesterol
Penmesterol is an orally active anabolic-androgenic steroid, a 17-alpha-methyltestosterone derivative bearing a 3-cyclopentyl enol ether, described in older European pharmacological literature. It behaves as a long-acting methyltestosterone-type oral androgen and is of largely historical interest.
01 Overview
Penmesterol is the 3-cyclopentyl enol ether of methyltestosterone, a modification intended to prolong action and improve oral handling. It appeared in mid-20th-century European formularies as an anabolic and androgen-replacement agent.
Human clinical data are scarce, and the compound never gained wide adoption. As a 17-alpha-methylated oral androgen it carries the hepatic and endocrine liabilities of that class; its properties are largely extrapolated from methyltestosterone.
02 Mechanism
Androgen-receptor agonist; a 3-cyclopentyl enol ether prodrug of 17-alpha-methyltestosterone giving oral activity and prolonged action.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Historical | 5–25 mg/day | Oral | Approximate figure from older European references; poorly documented. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Androgen replacement / anabolicUsed historically for androgen deficiency and anabolic support. | unquantified | Anecdotal | |
| Prolonged oral actionEnol-ether structure was intended to lengthen effect. | extended duration | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Estrogenic effectsGynaecomastia risk via methyltestosterone's aromatisation to methylestradiol. | Moderate | Expected | Preclinical | |
| HepatotoxicityCholestasis and enzyme elevation expected from the 17-alkylated methyltestosterone core. | Severe | Class effect | Preclinical |