Fluoxymesterone (Halotestin)

Fluoxymesterone, sold for decades under the brand name Halotestin, is a man-made anabolic-androgenic steroid (AAS) — a lab-made cousin of testosterone. You take it as a pill, and it’s built from testosterone with a chemical tweak (called 17α-methylation) that lets it survive being swallowed. It’s a steroid, not a peptide and not a SARM. It does have a real, FDA-approved medical past, but that past is mostly behind us. Here’s the catch: the strongest, best-documented evidence in people is about the harm it can do — mainly liver damage — not about any benefit. Using it without a prescription, or to boost performance, is illegal and banned in sport.

What it is

The full chemical name is 9-fluoro-17α-methyl-11β,17β-dihydroxyandrost-4-en-3-one (its molecular formula, the recipe of atoms, is C20H29FO3). Think of it as testosterone with three changes bolted on: a 17α-methyl group, a 9α-fluoro group, and an 11β-hydroxyl group. That 17α tweak is what lets it work as a pill — it stops the liver from breaking the drug down on the first pass through — but the very same feature is what makes this family of oral steroids hard on the liver (hepatotoxic).

How does it work in the body? Like other anabolic steroids, it latches onto and switches on the androgen receptor (AR), a docking site inside cells in muscle, prostate, skin, hair follicles, and bone. It leans heavily toward androgenic effects (the masculinizing, testosterone-like ones) and is fairly weak at the anabolic (muscle-building) side — so its anabolic-to-androgenic ratio is poor, roughly on par with plain testosterone rather than better. It also doesn’t aromatize: the 11β-hydroxyl group physically gets in the way of aromatase (the enzyme that turns androgens into estrogen), so unlike testosterone it doesn’t raise estradiol (a form of estrogen). Even so, gynecomastia (breast tissue growth in men) has still been reported occasionally through other routes.

The claims

The honest, legitimate claims are the ones on the FDA-approved label. In men, it was used as replacement therapy when the body isn’t making enough testosterone — primary hypogonadism (low testosterone from a problem in the testicles, either present from birth or acquired) and hypogonadotropic, or secondary, hypogonadism (low testosterone driven by the brain’s signaling) — and for delayed puberty in boys. In women, it was a palliative add-on (meant to ease symptoms, not cure) for androgen-responsive, recurrent metastatic breast cancer, in patients who met specific label criteria — postmenopausal, or with hormone-dependent tumors. All of these uses are now mostly a thing of the past.

In bodybuilding and athletic circles — off-label and illegal — people reach for fluoxymesterone for strength, aggression or “drive,” and a hard, dry look rather than for bulk. That fits its profile: strongly androgenic, non-estrogenic, and not a mass-builder. It’s often talked about as something taken right before a competition or a heavy lift. None of this is approved, it’s illegal without a prescription, and it’s banned in sport.

What the evidence actually shows

The evidence that it works is old and thin by today’s standards. The approved uses rest on clinical experience from the middle of the 20th century (hypogonadism replacement and breast-cancer palliation), not on modern, carefully controlled trials. There are no solid modern randomized controlled trials (RCTs — the gold-standard study design that randomly assigns who gets the drug) backing performance use, and the few medical roles it once had have been taken over by safer drugs.

The data we trust most in people is about harm, not benefit — specifically, how this 17α-alkylated family damages the liver. NIH’s LiverTox (a government database on drug-related liver injury) groups these C-17α-alkylated androgens together — and names Androxy/fluoxymesterone among them — as drugs linked to cholestasis (bile flow getting blocked), peliosis hepatis (blood-filled pockets in the liver), and, with long-term use, liver tumors. The broader science of how anabolic steroids work and what they do — including virilization (masculinizing changes) in women, the shutdown of the body’s own testosterone, and the world of “designer” steroids — is laid out thoroughly by Kicman (Br J Pharmacol 2008; PMID 18500378).

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

Legal and regulatory status

In the United States, fluoxymesterone is a prescription drug and a Schedule III controlled substance (it’s classed as an anabolic steroid). It’s one of the substances specifically listed as an anabolic steroid under the Anabolic Steroid Control Acts of 1990 and 2004, written into the Controlled Substances Act at 21 CFR 1308.13(f); its salts, esters, and ethers (related chemical forms) are Schedule III too. Having it without a valid prescription, or selling it for non-medical use, is a federal crime. For context, mesterolone is another Schedule III anabolic steroid listed in that same section.

It’s worth flagging one companion compound that often shows up next to performance steroids: 2,4-dinitrophenol (DNP). It is NOT approved for people to consume — the FDA declared it unfit for human consumption back in 1938. It’s an industrial chemical and a mitochondrial uncoupler (it sabotages the way cells produce energy), and it has a long, documented history of killing people through poisoning. DNP isn’t a federally scheduled controlled substance, but selling or marketing it for people to eat is illegal (it counts as adulterated/unapproved).

In sport, fluoxymesterone is on the WADA 2026 Prohibited List (WADA is the World Anti-Doping Agency) as an outside-the-body anabolic steroid under S1 (Anabolic Agents), category S1.1 — banned at all times, both in and out of competition — and it’s listed there as a named example (so is mesterolone). The related S4 section, Hormone and Metabolic Modulators (also banned at all times), covers aromatase inhibitors (drugs that block estrogen production, e.g., anastrozole, letrozole, exemestane, testolactone, formestane, aminoglutethimide); anti-estrogens/SERMs (selective estrogen receptor modulators, e.g., tamoxifen, raloxifene, toremifene; clomifene is listed under anti-estrogenic activity); myostatin modulators (which affect a protein that limits muscle growth); 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 banned (S4.4.2) for athletes who aren’t diabetic; using it therapeutically requires a TUE (a Therapeutic Use Exemption, official permission to use an otherwise-banned drug for a medical condition). DNP is banned in sport at all times too.

Safety

Fluoxymesterone comes with the full, serious risk profile you’d expect from a potent 17α-alkylated oral androgen.

• Liver damage (the signature danger of this class): Per NIH LiverTox and the FDA label — cholestatic hepatitis/jaundice (“bland cholestasis,” meaning bile backs up and the skin and eyes can turn yellow), which usually shows up within roughly 1 to 4 months of starting one of these C-17α-alkylated androgens and typically clears up once you stop; peliosis hepatis (blood-filled cysts in the liver that can burst and cause fatal bleeding, and may give no warning until it’s catastrophic); and, with prolonged use (often years), hepatic adenomas (benign liver tumors) and hepatocellular carcinoma (liver cancer).
• Heart and cholesterol: Oral 17α-alkylated androgens sharply lower HDL (“good” cholesterol) and raise LDL (“bad” cholesterol) — an atherogenic mix that promotes clogged arteries — and with long-term use can push up blood pressure and reshape the heart in harmful ways.
• Hormones: It suppresses the HPG axis (the hypothalamic-pituitary-gonadal axis — the brain-to-testes signaling loop), which lowers the body’s own testosterone and, in men, can shrink the testicles and harm sperm production and fertility.
• Virilization (in women) and effects in boys: Deepening voice, hirsutism (unwanted body and facial hair), changes to periods, and clitoromegaly (enlargement of the clitoris) — some of these don’t reverse. In boys, it can close the growth plates early (premature epiphyseal closure, which can stunt height) and trigger puberty too soon.
• Other: Acne, fluid retention/swelling (edema), mood and aggression changes, and polycythemia (too many red blood cells, which thickens the blood); also hypercalcemia (too much calcium in the blood), notably in patients who are immobilized and in breast-cancer patients — that one’s a labeled warning.

The compounds people commonly stack with anabolic steroids each carry serious, sometimes fatal, harms — and it’s worth being blunt about them:

• DNP (2,4-dinitrophenol) — this kills people. It uncouples oxidative phosphorylation (it short-circuits the cell’s energy-making process), which dumps the leftover energy out as uncontrolled heat (“runaway uncoupling”). That causes fatal overheating, racing heart, drenching sweat, and multi-organ failure. There is no antidote and no safe dose for people; deaths are well documented around the world, with reported fatalities climbing since 2000. It is never appropriate for anyone to consume.
• Insulin (misused by non-diabetics): Risk of severe, potentially deadly hypoglycemia (blood sugar crashing too low), seizures, permanent brain injury, and death — and it can hit fast and without warning. It’s one of the highest acute-fatality risks among the drugs people use alongside performance steroids.
• Aromatase inhibitors (anastrozole/letrozole/exemestane): By crushing estrogen, they speed up bone loss (osteoporosis) and fractures, worsen cholesterol, and cause joint pain and fatigue; using them off-label without monitoring only makes these worse.
• SERMs (tamoxifen/clomifene): Risk of venous thromboembolism — dangerous blood clots (DVT, a clot in a deep vein, and PE, a clot that travels to the lungs) — plus vision problems and mood effects; in its approved cancer use, tamoxifen has been linked to endometrial cancer (cancer of the uterine lining).
• T3 / thyroid hormone (liothyronine): Too much causes heart rhythm problems, racing heartbeat, atrial fibrillation (an irregular, often rapid heartbeat), and bone loss, and it can shut down your own thyroid; making sudden changes is dangerous.

Bottom line

Fluoxymesterone is a real but now largely outdated FDA-approved androgen whose strongest, best-documented human data are about liver injury, not benefit. Its approved jobs — treating hypogonadism, delayed puberty, and easing breast cancer — have all been replaced by safer drugs, and there’s no solid modern evidence it helps performance. It’s a Schedule III prescription steroid (the brand and generic are both discontinued in the US), banned at all times in sport under WADA S1.1, and it carries the full 17α-alkylated androgen risk profile: liver damage, cholesterol shifts that clog arteries, shutdown of the body’s testosterone signaling and infertility, and (in women and boys) masculinizing changes that may not reverse. 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: 8/10 · Good.

Sources

• NIH LiverTox — Androgenic Steroids (hepatotoxicity of 17α-alkylated AAS; names fluoxymesterone/Androxy)
• Halotestin (fluoxymesterone) FDA label — DailyMed
• Fluoxymesterone (DB01185) — DrugBank
• Kicman AT. 2008 — Pharmacology of anabolic steroids, Br J Pharmacol 154(3):502-521 (PMID 18500378)
• 21 CFR § 1308.13 — Schedule III anabolic steroids (eCFR)
• Federal Register — Implementation of the Anabolic Steroid Control Act of 2004
• DEA — Drug Scheduling
• WADA — The Prohibited List (2026 in force)
• USADA — What’s New on the 2026 WADA Prohibited List?
• Halotestin (Fluoxymesterone) — RxList
• ATSDR — Toxicological Profile for Dinitrophenols (2,4-DNP toxicity/lethality)