Halotestin
Also known as: Fluoxymesterone, Halo
Oral Anabolic Steroid | Extreme Strength & Aggression
Overview
Halotestin (fluoxymesterone) is a synthetic oral anabolic-androgenic steroid derived from testosterone, first introduced in the late 1950s by Upjohn under the brand name Halotestin. It is characterized by an extraordinarily high androgenic rating of approximately 1900 relative to testosterone, paired with an anabolic rating of roughly 1900 as well, though its real-world muscle-building effects are far less pronounced than these numbers suggest. The compound was originally FDA-approved for the treatment of male hypogonadism and advanced breast cancer in women, though it is rarely prescribed today due to the availability of safer alternatives. Fluoxymesterone does not aromatize to estrogen, meaning it produces no estrogenic side effects such as water retention or gynecomastia. In performance contexts, halotestin is used almost exclusively by advanced athletes and competitive bodybuilders in the final weeks before competition or powerlifting meets, where its ability to dramatically increase aggression, neural drive, and strength output without adding water weight makes it uniquely valuable. It is considered one of the harshest oral steroids with respect to hepatotoxicity and is unsuitable for general physique enhancement or beginner use.
Key benefits
- Dramatic increase in strength and power output without water retention
- Pronounced increase in aggression and competitive drive
- Does not aromatize to estrogen, producing a hard and dry appearance
- Enhances red blood cell production and oxygen-carrying capacity
- Rapid onset of effects, typically noticeable within days
- Uniquely suited for pre-competition or pre-meet peaking protocols
- Short cycle duration limits cumulative exposure
Mechanism of action
Fluoxymesterone exerts its effects primarily through exceptionally strong binding to the androgen receptor (AR), driven by its 9-alpha-fluoro and 11-beta-hydroxyl structural modifications that dramatically enhance receptor affinity beyond that of testosterone or DHT. Despite its extreme androgenic potency, it does not convert to estrogen via the aromatase enzyme, and its direct anabolic effect on skeletal muscle tissue is disproportionately low relative to its androgenic rating, likely due to rapid inactivation in muscle tissue. The compound's performance-enhancing effects are largely mediated through the central nervous system, increasing aggression, motivation, and perceived energy through androgen receptor activation in the brain. Fluoxymesterone also stimulates erythropoietin production, increasing red blood cell mass and oxygen-carrying capacity, which was the basis for its historical use in treating certain anemias. It enhances hemoglobin synthesis and may improve muscular endurance through improved oxygen delivery. The 17-alpha-methylation allows oral bioavailability but imposes significant hepatic stress, as the liver must process the intact steroid through first-pass metabolism. Fluoxymesterone suppresses endogenous testosterone production through negative feedback on the hypothalamic-pituitary-gonadal axis, and its extreme androgenic load can rapidly affect mood, lipid profiles, and prostate tissue.
Molecular data
- Type
- 9-fluoro-11-beta-hydroxy-17-alpha-methyltestosterone (C20H29FO3)
- Half-life
- ~9.5 hours
Indications
What the research community uses this compound for, with self-reported effectiveness.
Medical (Historical/Rare)
Performance (Advanced/Competition)
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 5-20 mg/day | Divided into 2-4 doses daily | — |
| — | 10-20 mg/day | Split into 2 doses (morning and 1-2 hours pre-training) | — |
| — | 10-20 mg/day | Split into 2 doses daily | — |
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Severe hepatic stress (elevated ALT, AST, GGT, bilirubin)
- Pronounced aggression and irritability
- HDL cholesterol suppression and LDL elevation
- Elevated blood pressure
- Headaches (frequently reported, may be related to blood pressure changes)
- Suppression of endogenous testosterone production
- Oily skin and acne
- Decreased appetite (potentially related to liver stress)
Rare side effects
- Cholestatic jaundice (dose-dependent, more likely with extended use or high doses)
- Peliosis hepatis (blood-filled cysts in the liver)
- Hepatocellular carcinoma (associated with prolonged use in historical medical settings)
- Severe mood disturbances or uncontrollable aggression
- Prostatic hypertrophy or exacerbation of benign prostatic hyperplasia
- Hair loss or accelerated male pattern baldness
- Prolonged HPTA suppression beyond expected recovery window
Contraindications
- Known or suspected prostate cancer
- Breast cancer in males
- Pregnancy (Category X - causes fetal harm)
- Active liver disease or existing hepatic impairment
- Severe cardiovascular disease or uncontrolled hypertension
- Hypercalcemia
- Nephrosis or nephrotic phase of nephritis
- History of cholestatic jaundice or hepatic dysfunction from prior anabolic steroid use
- Hypersensitivity to fluoxymesterone or any formulation component
Monitoring
- Liver function tests (ALT, AST, GGT, bilirubin, ALP): baseline, weekly during use, and 2-4 weeks post-discontinuation
- Lipid panel (total cholesterol, HDL, LDL, triglycerides): baseline and 2 weeks into use
- Blood pressure: daily self-monitoring during use
- Complete blood count with hematocrit: baseline and at cycle conclusion
- Total and free testosterone, LH, FSH: baseline and post-cycle to assess HPTA recovery
- Prostate-specific antigen (PSA) in men over 40: baseline and post-cycle
- Subjective mood and aggression monitoring throughout use
References
Primary literature and clinical-trial data informing this entry.