Anabolic steroidAndrogenOralDihydrotestosterone derivativeAntiestrogen

Mepitiostane

Also known as Thioderon · Epitiostanol methoxycyclopentyl ether

Written by enwyReviewed 5 Aug 20262 sources0 comments

Mepitiostane is an orally active anabolic steroid and antiestrogen derived from epitiostanol (a thioether DHT derivative), used in Japan under the brand Thioderon for breast cancer and to raise erythropoietin production. It is a prodrug of epitiostanol and behaves as both a mild androgen and an estrogen-receptor antagonist.

01 Overview

Mepitiostane is the 17-(1-methoxycyclopentyl) ether of epitiostanol, providing improved oral absorption. It was developed in Japan and marketed as Thioderon for hormone-responsive breast cancer, and has been studied for its ability to stimulate erythropoietin and treat certain anaemias.

Because it opposes estrogen at the receptor while providing modest androgenic activity, it is unusual among oral AAS. Human data exist but are largely confined to Japanese oncology and nephrology literature rather than sports-medicine trials.

02 Mechanism

Prodrug hydrolysed to epitiostanol, a 2,3-epithio DHT derivative that binds the androgen receptor and antagonises the estrogen receptor; also stimulates renal erythropoietin output.

03 Dosing

Tier	Dose	Route	Notes
Clinical (breast cancer)	10–30 mg/day	Oral	Japanese oncology dosing, often 10 mg 1-3x daily.

Ester comparison

Ester	Half-life	Injection freq.	Testosterone by mass

04 Effects

Effect	Magnitude	Evidence
Antiestrogenic activityDocumented objective responses in hormone-responsive breast cancer.	tumour response in ER-positive breast cancer	Clinical
Erythropoiesis stimulationIncreases erythropoietin and red cell mass, studied in renal anaemia.	raised haematocrit	Clinical
Mild anabolic effectWeak androgenic/anabolic action relative to mainstream AAS.	modest	Observational

05 Side effects

Effect	Severity	Frequency	Evidence
HepatotoxicityTransaminase elevations reported.	Mild	Occasional	Clinical
VirilisationAcne, hirsutism and voice changes reported in female patients.	Moderate	In women	Clinical
PolycythaemiaElevated haematocrit raising thrombotic risk.	Moderate	Dose-related	Clinical

06 Legal status

Prescription pharmaceutical

Marketed as Thioderon. · as of Jan 2026

United States

Schedule III controlled substance

Anabolic steroid classification. · as of Jan 2026

07 References

Mepitiostane in the treatment of advanced breast cancerCancer Chemotherapy and Pharmacology (Japanese oncology literature)

Effect of mepitiostane on erythropoiesis and renal anaemiaNephron / Japanese nephrology studies

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.