Anabolic steroidAndrogenAnabolic steroid17-alpha-alkylatedOralTestosterone derivative

Fluoxymesterone (Halotestin)

Also known as Halotestin · Halo · Fluoxymesterone · Ultandren · Haldren

Written by enwyReviewed 15 Jul 20262 sources0 comments

Fluoxymesterone ('Halotestin', 'Halo') is a 17α-methylated, 9α-fluoro, 11β-hydroxy derivative of testosterone with very high androgenic potency and negligible mass-building effect. It is prized among strength and combat athletes for sharp increases in strength, aggression and hardness at low body-weight impact, but is strongly hepatotoxic and harsh on lipids.

01 Overview

An old pharmaceutical androgen (approved for hypogonadism, delayed puberty and inoperable breast cancer), fluoxymesterone has a strongly androgenic, non-anabolic profile. It does not aromatise and does not add appreciable mass or water.

Recreationally it is used pre-competition by powerlifters, strongmen and fighters for a rapid boost in aggression, drive and strength without weight gain. Those benefits come with a very poor safety profile: pronounced hepatotoxicity, severe lipid deterioration and heightened aggression, so it is typically used briefly and at low doses.

02 Mechanism

Highly androgenic AR agonist; the 9α-fluoro and 11β-hydroxy groups plus 17α-methylation increase potency and oral activity while preventing aromatisation.

03 Dosing

Tier	Dose	Route	Notes
Therapeutic	5–20 mg/day	Oral	Historical clinical dosing.
Common	10–20 mg/day	Oral	Typical pre-competition strength range.
Heavy	20–40 mg/day	Oral	High dose; hepatic and lipid risk escalates steeply.

Ester comparison

Ester	Half-life	Injection freq.	Testosterone by mass

04 Effects

Effect	Magnitude	Evidence
Sharp strength and aggression increaseRapid boost in strength, drive and aggression, used before competition.		Observational
Increased hardness without weight gainNo water or appreciable mass; adds a dry, hard look.		Observational
Heightened aggression / irritabilityStrong androgenicity can produce irritability and mood disturbance.		Anecdotal

05 Side effects

Effect	Severity	Frequency	Evidence
Severe hepatotoxicityOne of the more hepatotoxic orals; associated with cholestasis and, with prolonged use, peliosis hepatis.	Severe	Common	Clinical
Severe adverse lipid changesMarked HDL suppression and cardiovascular strain.	Severe	Very common	Observational
HPTA suppressionStrong suppression of endogenous testosterone.	Severe	Universal	Clinical

06 Legal status

United States

Schedule III controlled substance

as of

United Kingdom

Class C controlled substance

as of

07 References

Fluoxymesterone - DrugBank recordDrugBank

Anabolic Steroids - LiverToxLiverTox, NIH

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.