History

Fluoxymesterone was first described and synthesized in 1956 and introduced for medical use in the late 1950s by Upjohn (later Pharmacia & Upjohn) under the brand name Halotestin. As a Schedule CIII product it was FDA-approved for testosterone-deficiency conditions in men — primary and hypogonadotropic (secondary) hypogonadism and delayed male puberty — and as a palliative adjunct for androgen-responsive, recurrent metastatic breast cancer in women meeting the label's criteria. Both the brand Halotestin and the generic Androxy have since been discontinued in the United States; the molecule remains scheduled and prescription-only but is little used clinically, having been superseded by transdermal and injectable testosterone (better tolerated and less hepatotoxic) and, for breast cancer, by modern endocrine therapies.

Fluoxymesterone, sold for decades under the brand name Halotestin, is a synthetic anabolic-androgenic steroid (AAS). It is an orally active, 17α-methylated derivative of testosterone — a steroid, not a peptide and not a SARM. It has a real but now largely historical FDA-approved medical pedigree, yet its strongest, best-documented human evidence concerns harm — specifically liver injury — rather than benefit. Non-medical and performance use is illegal without a prescription and banned in sport.

What it is

Fluoxymesterone is 9-fluoro-17α-methyl-11β,17β-dihydroxyandrost-4-en-3-one (molecular formula C20H29FO3). Structurally it is testosterone with three modifications: a 17α-methyl group, a 9α-fluoro substituent, and an 11β-hydroxyl group. The 17α-alkylation is what makes it orally bioavailable — it resists first-pass hepatic breakdown — and that same feature is responsible for the hepatotoxicity characteristic of this class of oral steroids.

Mechanistically, like other AAS it binds and activates the intracellular androgen receptor (AR) in target tissues (muscle, prostate, skin, hair follicle, bone). It is strongly androgenic with comparatively modest anabolic activity; its anabolic-to-androgenic ratio is poor, roughly testosterone-like rather than favorable. It is non-aromatizable: steric hindrance from the 11β-hydroxyl group blocks conversion to estrogen by aromatase, so unlike testosterone it does not raise estradiol (although gynecomastia has still occasionally been reported via other mechanisms).

The claims

The FDA-approved label uses are the legitimate medical claims. In men, it was indicated as replacement therapy in testosterone-deficiency conditions — primary hypogonadism (congenital or acquired) and hypogonadotropic (secondary) hypogonadism — and for delayed male puberty. In women, it was a palliative adjunct for androgen-responsive, recurrent metastatic breast cancer (per the label, in women meeting specific postmenopausal criteria or with hormone-dependent tumors). These uses are now largely historical.

In bodybuilding and athletic circles (off-label and illicit), fluoxymesterone is valued for strength, aggression or “drive,” and a hard, dry look rather than mass — consistent with its strongly androgenic, non-estrogenic, non-mass-building profile. It is commonly described as a pre-competition or pre-lift compound. This use is unapproved, illegal without a prescription, and banned in sport.

What the evidence actually shows

The efficacy evidence is old and thin by modern standards. The approved indications rest on mid-20th-century clinical experience (hypogonadism replacement and breast-cancer palliation), not on contemporary randomized trials. There are no robust modern RCTs supporting performance use, and the drug’s narrow therapeutic role has been displaced by safer agents.

The best-characterized human data are on harm, not benefit — specifically the hepatotoxicity of the 17α-alkylated class. NIH’s LiverTox explicitly groups the C-17α-alkylated androgens (the entry names Androxy/fluoxymesterone among them) with agents implicated in cholestasis, peliosis hepatis, and, with prolonged use, hepatic tumors. General AAS pharmacology and effects — including virilization in women, suppression of endogenous testosterone, and the designer-steroid context — are reviewed authoritatively by Kicman (Br J Pharmacol 2008; PMID 18500378).

Bottom line on evidence: fluoxymesterone has a genuine but old efficacy record in its approved medical roles, no credible modern evidence for performance use, and its most solid human data document liver injury.

Legal and regulatory status

In the United States, fluoxymesterone is a prescription drug and a Schedule III controlled substance (anabolic steroid). It is among the substances enumerated as anabolic steroids under the Anabolic Steroid Control Acts of 1990 and 2004, codified in the Controlled Substances Act at 21 CFR 1308.13(f); salts, esters, and ethers are likewise Schedule III. Possession without a valid prescription and non-medical distribution are federal offenses. For context, mesterolone is also a Schedule III anabolic steroid enumerated in the same section.

It is worth flagging a companion compound that often appears alongside performance steroids: 2,4-dinitrophenol (DNP) is NOT approved for human consumption — the FDA declared it unfit for human consumption in 1938. It is an industrial chemical and mitochondrial uncoupler with a long, documented history of fatal poisonings. DNP is not a federally scheduled controlled substance, but its sale or marketing for human consumption is unlawful (adulterated/unapproved).

In sport, fluoxymesterone is on the WADA 2026 Prohibited List as an exogenous AAS under S1 (Anabolic Agents), category S1.1 — banned at all times, in and out of competition — and is a named example under S1.1 (as is mesterolone). The related S4 section, Hormone and Metabolic Modulators (also banned at all times), covers aromatase inhibitors (e.g., anastrozole, letrozole, exemestane, testolactone, formestane, aminoglutethimide), anti-estrogens/SERMs (e.g., tamoxifen, raloxifene, toremifene; clomifene listed under anti-estrogenic activity), myostatin modulators, and metabolic modulators (S4.4): AMPK activators such as AICAR (S4.4.1), insulins and insulin-mimetics (S4.4.2), meldonium (S4.4.3), and trimetazidine (S4.4.4). New for 2026, BAM15 was added as an example AMPK-related metabolic modulator, and 2-phenylbenzo[h]chromen-4-one (α-naphthoflavone) was added as a new aromatase-inhibitor example. Insulin is prohibited (S4.4.2) for non-diabetic athletes; therapeutic use requires a TUE. DNP is also prohibited in sport at all times.

Safety

Fluoxymesterone carries the full and serious risk profile of a potent 17α-alkylated oral androgen.

Hepatotoxicity (the signature danger of this class): Per NIH LiverTox and the FDA label, cholestatic hepatitis/jaundice (“bland cholestasis”), typically arising within roughly 1 to 4 months of starting a C-17α-alkylated androgen and usually reversible on discontinuation; peliosis hepatis (blood-filled hepatic cysts that can rupture and cause fatal hemorrhage, and can be silent until catastrophic); and hepatic adenomas and hepatocellular carcinoma with prolonged use (often years).
Cardiovascular and lipids: Oral 17α-alkylated androgens markedly lower HDL and raise LDL — an atherogenic profile — with possible blood-pressure elevation and adverse cardiac remodeling under chronic use.
Endocrine: Suppression of the HPG axis, reducing endogenous testosterone, with testicular atrophy and impaired spermatogenesis/fertility in men.
Virilization (women) and effects in boys: Deepening voice, hirsutism, menstrual changes, and clitoromegaly — some effects irreversible. In boys, premature epiphyseal closure and precocious sexual development.
Other: Acne, fluid retention/edema, mood and aggression changes, polycythemia; hypercalcemia notably in immobilized patients and breast-cancer patients (a labeled warning).

The compounds people commonly pair with AAS each carry serious, sometimes fatal, harms — and it is worth being blunt about them:

DNP (2,4-dinitrophenol) — this kills people. It uncouples oxidative phosphorylation, generating uncontrolled heat (“runaway uncoupling”). It causes fatal hyperthermia, tachycardia, profuse sweating, and multi-organ failure. There is no antidote and no safe therapeutic margin for human use; deaths are well documented internationally, with reported fatalities rising since 2000. It is never appropriate for human consumption.
Insulin (non-diabetic misuse): Risk of severe, potentially lethal hypoglycemia, seizures, irreversible brain injury, and death — onset can be rapid and unpredictable. One of the highest acute-fatality risks among PED-adjacent agents.
Aromatase inhibitors (anastrozole/letrozole/exemestane): Estrogen suppression drives accelerated bone loss/osteoporosis and fractures, adverse lipid shifts, arthralgia, and fatigue; off-label, unmonitored use compounds these.
SERMs (tamoxifen/clomifene): Venous thromboembolism (DVT/PE) risk, visual disturbances, and mood effects; tamoxifen carries an endometrial-cancer signal in approved oncology use.
T3 / thyroid hormone (liothyronine): Excess causes cardiac arrhythmias, tachycardia, atrial fibrillation, and bone loss, and can suppress endogenous thyroid function; abrupt changes are hazardous.

Bottom line

Fluoxymesterone is a genuine but now largely obsolete FDA-approved androgen whose strongest, best-documented human data concern liver injury rather than benefit. Its approved roles — hypogonadism, delayed puberty, and breast-cancer palliation — have been superseded by safer agents, and there is no robust modern evidence for performance use. It is a Schedule III prescription steroid (brand and generic discontinued in the US), banned at all times in sport under WADA S1.1, and it carries the full 17α-alkylated androgen risk profile: hepatotoxicity, atherogenic lipid shifts, HPG-axis suppression and infertility, and (in women and boys) irreversible virilization. The supporting compounds people pair with it — DNP, insulin, aromatase inhibitors, SERMs, and T3 — each carry serious, sometimes fatal, risks; DNP in particular has no antidote and kills people. It is a steroid, not a peptide.

Evidence grade: Preliminary human.

Fluoxymesterone (Halotestin)