Title: Fluoxymesterone
CAS Registry Number: 76-43-7
CAS Name: (11b,17b)-9-Fluoro-11,17-dihydroxy-17-methylandrost-4-en-3-one
Additional Names: 11b,17b-dihydroxy-9a-fluoro-17a-methyl-4-androsten-3-one; 9a-fluoro-11b-hydroxy-17a-methyltestosterone
Trademarks: Halotestin (Pfizer)
Molecular Formula: C20H29FO3
Molecular Weight: 336.44
Percent Composition: C 71.40%, H 8.69%, F 5.65%, O 14.27%
Literature References: Prepn: Herr et al., J. Am. Chem. Soc. 78, 501 (1956). cf. Herr, US 2813881 (1957 to Upjohn). Comprehensive description: J. Kirschbaum, Anal. Profiles Drug Subs. 7, 251-275 (1978).
Properties: Crystals, dec 270°. [a]D +109° (ethanol). uv max (ethanol): 240 nm (e 16700). Sol in pyridine; slightly sol in acetone, chloroform; sparingly sol in methanol. Practically insol in water, ether, benzene, hexanes.
Optical Rotation: [a]D +109° (ethanol)
Absorption maximum: uv max (ethanol): 240 nm (e 16700)
NOTE: This is a controlled substance (anabolic steroid): 21 CFR, 1308.13, as defined in 1300.01.
Therap-Cat: Androgen.
Keywords: Androgen.
Flupentixol Fluperolone Acetate Fluphenazine Flupirtine Fluprednidene Acetate

Systematic (IUPAC) name
Clinical data
AHFS/Drugs.com monograph
MedlinePlus a682690
Pregnancy cat. X
Legal status Schedule III Controlled Substance
Pharmacokinetic data
Bioavailability 100% Oral
Metabolism Hepatic
Half-life 9.5 hours
Excretion urine
CAS number 76-43-7 YesY
ATC code G03BA01
PubChem CID 6446
IUPHAR ligand 2861
DrugBank DB01185
ChemSpider 6205 YesY
KEGG D00327 YesY
Chemical data
Formula C20H29FO3 
Mol. mass 336.441 g/mol
 YesY (what is this?)  (verify)

Fluoxymesterone (trade name Halotestin) is an anabolic steroid with strong androgenic properties that has been used in the treatment of male hypogonadism, delayed puberty in males, and in the treatment of breast neoplasms in women. It is approximately 5 times as potent as methyltestosterone.[citation needed] The antitumor activity of fluoxymesterone appears related to reduction or competitive inhibition of prolactin receptors or estrogen receptors or production.[citation needed]

Like many C-17 alpha alkylated steroids, fluoxymesterone has poor binding to the androgen receptor. Even so, its actions are mediated by the androgen receptor, most-likely due to its prolonged plasma half-life.[1]

It is considered a very toxic oral drug.

Though the half-life of fluoxymesterone is about 9.2 hours.[citation needed]