Fluoxymesterone, sold under the brand names Halotestin and Ultandren among others, is an androgen and anabolic steroid (AAS) medication which is used in the treatment of low testosterone levels in men, delayed puberty in boys, breast cancer in women, and anemia. It is taken by mouth.
Side effects of fluoxymesterone include symptoms of masculinization like acne, increased hair growth, voice changes, and increased sexual desire. It can also cause liver damage and cardiovascular side effects like high blood pressure. The drug is a synthetic androgen and anabolic steroid and hence is an agonist of the androgen receptor (AR), the biological target of androgens like testosterone and dihydrotestosterone (DHT). It has strong androgenic effects and moderate anabolic effects, which make it useful for producing masculinization.
Fluoxymesterone was first described in 1956 and was introduced for medical use in 1957. In addition to its medical use, fluoxymesterone is used to improve physique and performance. The drug is a controlled substance in many countries and so non-medical use is generally illicit.Fluoxymesterone is or has been used in the treatment of hypogonadism, delayed puberty, and anemia in males and the treatment of breast cancer in women. It is specifically approved in one or more countries for the treatment of hypogonadism in men, delayed puberty in boys, and breast cancer in women. Current prescribing guidelines in the United States list only the treatment of androgen deficiency in males and breast cancer in females as indications.[1As an AAS, fluoxymesterone is an agonist of the androgen receptor (AR), similarly to androgens like testosterone and DHT. It is a substrate for 5α-reductase like testosterone, and so is potentiated in so-called "androgenic" tissues like the skin, hair follicles, and prostate gland via transformation into 5α-dihydrofluoxymesterone. As such, fluoxymesterone has a relatively poor ratio of anabolic to androgenic activity similarly to testosterone and methyltestosterone. However, fluoxymesterone is nonetheless proportionally less androgenic and more anabolic than methyltestosterone and testosterone.
Fluoxymesterone has been reported to be non-aromatizable due to steric hindrance by its C11β hydroxyl group, and hence is not considered to have a propensity for producing estrogenic effects such as gynecomastia or fluid retention. However, paradoxically, a case report of severe fluoxymesterone-induced gynecomastia exists, and gynecomastia associated with fluoxymesterone has also been reported in other publications, although this may not be due to estrogenic activity. Fluoxymesterone is thought to possess little or no progestogenic activity.
Because of the presence of its 17α-methyl group, the metabolism of fluoxymesterone is impeded, resulting in it being orally active, although also hepatotoxic.
Fluoxymesterone has been found to act as a potent inhibitor of 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) (IC50 = 60–630 nM), with a potency comparable to that of the 11β-HSD2 inhibitor glycyrrhetinic acid. This action of fluoxymesterone is unique among AAS and is likely related to its 11β-hydroxyl group. 11β-HSD2 is responsible for the inactivation of the glucocorticoids cortisol and corticosterone (into cortisone and 11-dehydrocorticosterone, respectively). Inhibition of 11β-HSD2 by fluoxymesterone may result in mineralocorticoid receptor overactivation and associated side effects such as hypertension and fluid retention, and has been hypothesized to be involved in the cardiovascular and other adverse effects of fluoxymesterone.This medication is used in men who do not make enough of a natural substance called testosterone. In males, testosterone is responsible for many normal functions, including growth and development of the genitals, muscles, and bones. It also helps cause normal sexual development (puberty) in boys. Fluoxymesterone is similar to the natural testosterone produced by your body. It belongs to a class of drugs known as androgens. It works by affecting many body systems so that the body can develop and function normally.
Fluoxymesterone may also be used in certain adolescent boys to cause puberty in those with delayed puberty.