Halotestin (Fluoxymesterone)
Fluoxymesterone
Fluoxymesterone, marketed historically as Halotestin, is an orally active anabolic-androgenic steroid derived from testosterone. It is a C17-alpha-alkylated compound with fluorine at the 9-alpha position and a hydroxyl at 11-beta, giving it high oral bioavailability and very high androgenic potency. Developed by Upjohn and introduced in 1957, it was approved for hypogonadism, delayed puberty, and later for breast cancer in women. It is a Schedule III controlled substance in the United States.
Split daily dose AM and pre-training given the ~9 hour half-life. Maximum cycle duration 2-4 weeks due to severe hepatotoxicity. Liver enzymes MUST be checked pre and post. Have a testosterone base running - halotestin suppresses endogenous testosterone rapidly.
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
How it works
Fluoxymesterone binds the androgen receptor (AR) with very high affinity and drives strong androgenic signaling. Its anabolic contribution to muscle mass is relatively modest compared to other AAS, but its effect on the central nervous system, aggression, and strength expression is pronounced.
It does not aromatize to estrogen due to the 9-alpha-fluorine substitution, but it has weak progestogenic activity and may bind the progesterone receptor at high doses. It does not produce water retention, and gyno risk is low from fluoxymesterone itself.
The C17-alpha-alkyl group protects it from first-pass hepatic metabolism (high oral bioavailability) but also imparts severe hepatotoxicity - among the worst of any AAS. Cholestatic jaundice and hepatic lesions have been documented with relatively short courses. Lipid shift (severe HDL drop, severe LDL rise) is also extreme. Endogenous testosterone suppression is rapid and complete.
What to expect
First 3-5 days: noticeable mood and aggression change, mental intensity increase. Strength in the gym begins to rise quickly.
Week 2-3: peak strength effect on competitive lifts. Mental intensity peaks. Cardiovascular and hepatic stress accumulating.
Week 3-4 (end of cycle): sustained strength but diminishing marginal return. Strongly advised to stop at 4 weeks maximum due to hepatic and lipid burden.
Evidence
References for this compound are being re-checked against their source records. We are not showing them until each one is confirmed to support the claim it sits under.
Side effects & safety
Commonly reported
- Elevated liver enzymes (ALT/AST) - often severe, 3-6x ULN within 2-4 weeks
- Severe lipid shift (HDL drop 30-50%, LDL rise 30-50%)
- Marked aggression and mood changes
- Suppression of endogenous testosterone (rapid and complete)
- Oily skin and acne
Less common & notes
- Hair loss acceleration (severe in genetically predisposed users), insomnia, anxiety, headaches, elevated blood pressure, nausea.
- Women: very high virilization risk - contraindicated except for historical supervised breast cancer use.
- Rare but serious: cholestatic jaundice (can occur after 2-3 weeks), hepatic adenoma, peliosis hepatis, hepatocellular carcinoma with prolonged use, severe cardiovascular events from lipid shifts, violent behavior episodes in susceptible users.
Pharmacokinetics
Oral
Per dose - supports 1-2x daily dosing
Hepatic (CYP3A4, CYP2C9). Renal excretion of metabolites.
Storage. Store at controlled room temperature (20-25°C / 68-77°F). Protect from moisture and light. Keep in original container with desiccant when available. Keep out of reach of children and in a locked location - Schedule III controlled substance in the United States.
Regulatory status
Schedule III controlled substance in the United States under the Anabolic Steroids Control Act of 1990. Historically FDA-approved (brand name Halotestin, Upjohn/Pharmacia) for hypogonadism, delayed puberty, and advanced breast cancer. The brand was discontinued though generic fluoxymesterone may still be available by prescription. Possession or distribution without a valid prescription is a federal offense in the United States.
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