Peptide & Experimental
Fluoxymesterone (Halotestin)
Oral anabolic-androgenic steroid, 17α-alkylated and fluorinated; formerly approved in the US · Halotestin, Ora-Testryl, Android-F, Fluoxymesterone, 9α-fluoro-11β-hydroxy-17α-methyltestosterone
Fluoxymesterone is an androgen in tablet form that was approved in the US in 1956 as Halotestin – for men with testosterone deficiency or delayed puberty and for women with advanced breast cancer. Oncology provides randomized studies with several hundred patients, and pediatrics provides long-term data on growth. There is not a single study on muscle building or strength in healthy people.
In short
Fluoxymesterone was an approved medicine for decades, and that makes it comparatively well studied among the oral steroids. In a randomized study with 238 women with metastatic breast cancer, 53 instead of 42 percent responded when it was added to tamoxifen; there was no survival benefit. After breast cancer surgery, it brought no benefit in a study with 541 women. In boys with delayed growth, it accelerated linear growth without reducing final height. Data on muscle, strength or performance in healthy people are lacking. The prescribing information clearly warns of liver damage up to and including tumors; in the US, no product is on the market any longer, and in Germany the substance is prescription-only and is listed in the annex of the Anti-Doping Act.
What fluoxymesterone is and how it works
Fluoxymesterone is a modified testosterone. A methyl group at position 17α protects it from rapid breakdown in the liver and makes it effective as a tablet; in addition, there is a fluorine atom at position 9 and a hydroxyl group at position 11. In the US it came onto the market in 1956 as Halotestin from Upjohn, later followed by other products such as Ora-Testryl and Android-F. According to the FDA database, none of them is marketed today.
Like all anabolic-androgenic steroids, fluoxymesterone binds to the androgen receptor. The prescribing information lists protein synthesis, retention of nitrogen, sodium and phosphorus, the typical masculinizing effects and stimulation of blood formation. Through feedback to the pituitary gland, the release of LH and thus the body’s own testosterone production falls, and at high doses also sperm production. The half-life after ingestion is about 9.2 hours. An overview of the entire substance group can be found under Anabolic steroids (AAS).
What is well supported
Its role as a medicine is well supported. Fluoxymesterone was approved in the US for three uses: as replacement for absent or too low testosterone, for confirmed delayed puberty in boys, and for palliation of recurrent, androgen-sensitive breast cancer in women. In oncology, it was tested in randomized studies against and together with tamoxifen; the combination showed a biological effect but no survival benefit. In pediatrics, long-term data on growth are available. The warning profile of the prescribing information, especially for the liver, is also well documented.
What the studies show
Metastatic breast cancer: in addition to tamoxifen
Ingle 1988 randomly assigned 238 postmenopausal women with metastatic breast cancer to tamoxifen alone or tamoxifen plus fluoxymesterone. With the combination, 53 percent responded; with tamoxifen alone, 42 percent. Median time to progression was 350 versus 199 days, but the difference was not statistically significant. Duration of response and survival did not differ, and androgenic side effects were more frequent with the combination. Of the women who received fluoxymesterone alone after tamoxifen failure, 21 of 52 responded. The authors saw a genuine biological effect, but not a sufficient reason for routine use.
After breast cancer surgery
In a follow-up study with 541 women after surgery for hormone-sensitive breast cancer, fluoxymesterone in addition to tamoxifen brought no significant benefit in relapse-free survival or overall survival over 11.4 years of follow-up; the hazard ratio for relapse or death was 0.84 with a confidence interval of 0.64 to 1.10. As expected, more masculinization occurred in the women taking fluoxymesterone (Ingle 2006).
Cancer-related wasting
In patients with loss of appetite and weight loss due to cancer, a randomized study compared fluoxymesterone with megestrol acetate and dexamethasone. Fluoxymesterone increased appetite considerably less and did not have a favorable side-effect profile; the authors clearly call it the inferior choice (Loprinzi 1999).
Growth and puberty in boys
A prospective study followed 82 short boys with delayed growth and delayed puberty or familial short stature who received low-dose fluoxymesterone for 6 to 60 months, and compared the predictions with 34 untreated boys. During treatment, the boys grew 1.7 to 2.5 times as fast as before; undesirable androgenic effects or overly rapid puberty were not observed. Final height was on average 5 to 6 cm above the prediction made before the start of treatment (Strickland 1993). There was no random assignment.
Where the data stop
All controlled studies concern sick people: women with breast cancer, cancer patients with wasting, children with delayed growth. There is no study that tests fluoxymesterone in healthy men for muscle mass, strength or performance, and none that compares it with testosterone or another steroid for this purpose.
The safety data also have gaps. The warnings in the prescribing information on the liver apply to the 17α-alkylated androgens as a group; how often cholestasis or tumors occur specifically with fluoxymesterone has not been quantified. Systematic measurements of blood lipids, the heart and blood vessels are lacking. The studies are also old, and the product has not been on the market for years, so no new data from medicine are being added.
Status, approval and legal
In Germany, fluoxymesterone is prescription-only (Annex 1 of the German Medicines Prescription Ordinance, AMVV); no finished medicinal product approved here was found during research. In the US, it was approved in 1956 as Halotestin (NDA 010611); according to the FDA database, Halotestin and all other fluoxymesterone products approved there are no longer marketed (as of 10/2026). There it is a Schedule III controlled substance.
Fluoxymesterone is listed by name in the annex of the German Anti-Doping Act. Manufacture, trade, supply and prescription for doping purposes are prohibited, as are acquisition, possession and bringing into the country of non-small quantities for doping in sport. On the WADA Prohibited List 2026, it is listed under S1.1 and is prohibited at all times.
Safety
The prescribing information warns above all about the liver: with 17α-alkylated androgens, cholestasis with jaundice can occur, which resolves after discontinuation; after long-term, high-dose administration, liver adenomas, hepatocellular carcinoma and peliosis hepatis have been described, a condition with blood-filled cavities in the liver. All three can be life-threatening, which is why the prescribing information calls for regular liver tests. A review of liver damage caused by anabolic-androgenic steroids confirms this picture for the entire group and emphasizes that the liver usually recovers, but some consequences remain (Petrovic 2022).
Further points from the prescribing information: fluid retention up to heart failure in pre-existing heart, kidney or liver disease, too many red blood cells, a possible rise in cholesterol and an enhanced effect of anticoagulants. In men, breast growth, too frequent or too prolonged erections and, at high doses, a reduced sperm count can occur. In women, deepening of the voice and enlargement of the clitoris are usually not reversible. It also lists headache, anxiety and depression. For the substance group as a whole, heart damage and the shutdown of the body’s own hormone production have been documented in large cohorts, see Anabolic steroids (AAS).
BK-Score Supported, with caveats
| Human evidence | 6 | |
|---|---|---|
| Mechanism | 7 | |
| Safety data | 5 | |
| Hype gap | 4 | |
| Track record of use | 6 |
Evidence 6, because fluoxymesterone has been tested in randomized studies in humans – in metastatic breast cancer with 238 women (response 53 versus 42 percent in addition to tamoxifen, Ingle 1988), after breast cancer surgery with 541 women (no benefit, Ingle 2006) and in cancer-related wasting (inferior, Loprinzi 1999) – but no study exists for muscle mass, strength or performance in healthy people. Mechanism 7, because the androgen receptor, suppression of the hormonal axis and the liver strain from 17α-alkylation are known and the prescribing information describes the mode of action and half-life, but the significance of the fluorination in humans has not been specifically measured. Safety 5, because the US prescribing information contains a detailed warning profile – cholestasis, liver tumors, peliosis hepatis, polycythemia, masculinization – and the cancer studies recorded side effects, but systematic liver and blood lipid measurements for this substance are lacking; the number means moderately studied, not harmless. Hype 4, because the effect in medicine is real, but neither efficacy nor safety data exist for use outside medicine. Use 6, because fluoxymesterone was used by physicians for decades from 1956 onwards, but today it is no longer marketed in the US and no finished medicinal product is listed in Germany. Direction mixed: proven but limited effect in oncology, no evidence for healthy people, plus a clearly described liver risk. For comparison: oxymetholone (7/8/7/4/7), stanozolol (6/7/7/3/6), mesterolone (5/7/6/4/8).
The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)
Frequently asked questions about fluoxymesterone
What is fluoxymesterone?
An androgen in tablet form, a modified testosterone with a methyl and a fluorine group. In the US, it was approved from 1956 as Halotestin, among other things for testosterone deficiency, delayed puberty and advanced breast cancer.
Is the effect on muscle and strength proven?
No. The controlled studies come from oncology and pediatrics. There is no study on muscle mass, strength or performance in healthy people.
What do the breast cancer studies show?
In metastatic breast cancer, 53 instead of 42 percent of women responded when it was added to tamoxifen; there was no survival benefit. After breast cancer surgery, the combination brought no significant benefit in a study with 541 women.
How hard is fluoxymesterone on the liver?
The prescribing information warns of cholestasis with jaundice and, after long-term, high-dose administration, of liver tumors and peliosis hepatis. How often this occurs specifically with fluoxymesterone has not been quantified.
Is fluoxymesterone permitted in Germany?
It is prescription-only; no approved finished medicinal product was found. The substance is listed in the annex of the Anti-Doping Act, and in sport it is prohibited at all times.
Related
- Related topicOxymetholone (Anadrol)
- Related topicMetenolone (Primobolan)
- Related topicDrostanolone (Masteron)
- Related topicStanozolol (Winstrol)
- Related topicOxandrolone (Anavar)
- Related topicMethyltrienolone (metribolone, R1881)
Sources
- Prescribing information Halotestin (fluoxymesterone), US label as of 05/2002 (DailyMed) – indications, warnings on liver, blood and masculinization
- FDA, Drugs@FDA – Halotestin, NDA 010611: approval 1956, status discontinued
- Ingle JN et al., J Clin Oncol 1988 – RCT: tamoxifen alone or with fluoxymesterone in metastatic breast cancer, 238 women
- Ingle JN et al., Breast Cancer Res Treat 2006 – RCT: tamoxifen alone or with fluoxymesterone after breast cancer surgery, 541 women
- Loprinzi CL et al., J Clin Oncol 1999 – RCT: megestrol acetate, dexamethasone or fluoxymesterone in cancer-related wasting
- Strickland AL, Pediatrics 1993 – long-term results of low-dose fluoxymesterone in delayed growth and delayed puberty, 82 boys
- Petrovic A et al., World J Gastroenterol 2022 – liver damage caused by anabolic-androgenic steroids (review)
- German Medicines Prescription Ordinance (AMVV), Annex 1 – prescription requirement
- German Anti-Doping Act (AntiDopG), § 2, § 4 and annex
- NADA – Prohibited List 2026, informational German translation (S1.1 anabolic-androgenic steroids)
Open in the database – with search, filters and comparison (German app)
Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-10-07.