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muscle diagramFluoxymesterone is more popularly known by its brand name, Halotestin or Halo for short. Halotestin is actually derived from cortisol (a glucocorticoid) and as you can see from its structure, shares the C-11 hydroxyl (OH) group with cortisol-like steroids. The binding affinity of halotestin for the androgen receptor is very lowbut contrary to popular belief, its androgenic effects are still mediated through the androgen receptor1. Halotestin cannot be converted to estrogenic metabolites but is converted to a more potent 5-alpha reduced form2. The half-life of the parent compound is a little more than 9 hours but the presence of active metabolites (such as the 5-alpha reduced form) likely prolongs the active half-life3.

Halotestin is known to be very androgenic and quite liver toxic. This steroid is rumored to be good in a “cutting stack” because it seems to not put on much weight but keeps a physique hard and increases aggression to get through workouts on low calories. Some evidence suggests that halotestin is a potent glucocorticoid antagonist. Like oxandrolone, halotestin actually increases total and free cortisol levels while slightly reducing corticosteroid binding globulin (CBG) levels4. CBG is a binding protein similar to sex hormone binding globulin (SHBG) that removes corticosteroids (like cortisol) from the blood and acts as a reservoir to resupply the blood if cortisol levels fall. Small changes in CBG levels can dramatically alter free plasma levels of cortisol. Obviously the effects of halotestin on glucocorticoid signaling are quite complicated and difficult to dissect. In any case, the likely scenario is that halotestin is anticatabolic with strong androgenic activity.

Halotestin binds somewhat weakly to SHBG but is still capable of displacing estradiol and testosterone at higher doses1,5,6.  The strong androgenic activity and lack of aromatization to estrogenic metabolites can result in reductions in plasma levels of SHBG which may result in estrogenic side effects due to higher free levels of estrogens7. Additionally, halotestin has a rather large suppressive effect on thyroid binding globulin levels with only moderate compensatory increases in thyroxine-binding prealbumin which is likely to cause higher plasma levels of T4 and T3 with greater T3 uptake4. These effects on thyroid hormones and binding proteins may help to explain the effectiveness of this drug in a “cutting” stack. Halotestin has been shown to be as effective as oxymetholone in elevating red blood cell levels in the scientific literature8,9. Halotestin is available in the US and in other countries, especially Mexico as a pharmaceutical preparation as well as through black market suppliers. An interesting use of halotestin includes the use of a 5-alpha reductase inhibitor, like finasteride. The purpose of such a combination would be to harness the anticatabolic activity of halotestin while reducing some of the harsher androgenic side effects.

Other names include: Anadroid-F, Androsterolo, Fluosterone, Fluotestin, Flusteron, Flutestos, Neo-Ormonal, Ora Testryl, Oralsterone, Oratestin, Testoral, Ultandren, Ultandrene

1. Saartok T, Dahlberg E, Gustafsson JA: Relative binding affinity of anabolic-androgenic steroids: comparison of the binding to the androgen receptors in skeletal muscle and in prostate, as well as to sex hormone-binding globulin. Endocrinology, 1984;114(6):2100-6.

2. Kammerer RC, Merdink JL, Jagels M, Catlin DH, Hui KK: Testing for fluoxymesterone (Halotestin) administration to man: identification of urinary metabolites by gas chromatography-mass spectrometry. J Steroid Biochem, 1990;36(6):659-66.

3. Capponi VJ, Cox SR, Harrington EL, Wright CE, Antal EJ, Albert KS. Liquid chromatographic assay for fluoxymesterone in human serum with application to a preliminary bioavailability study. J Pharm Sci, 1985;74(3):308-11.

4. Barbosa J, Seal US, Doe RP: Effects of anabolic steroids on hormone-binding proteins, serum cortisol and serum nonprotein-bound cortisol. J Clin Endocrinol Metab, 1971;32(2):232-40.

5. Pugeat MM, Dunn JF, Nisula BC: Transport of steroid hormones: interaction of 70 drugs with testosterone-binding globulin and corticosteroid-binding globulin in human plasma. J Clin Endocrinol Metab, 1981;53(1):69-75.

6. Vigersky RA, Easley RB, Loriaux DL. Effect of fluoxymesterone on the pituitary-gonadal axis: the role of testosterone-estradiol-binding globulin. J Clin Endocrinol Metab, 1976;43(1):1-9.

7. Wasserman P, Segal-Maurer S, Rubin D. Low sex hormone-binding globulin and testosterone levels in association with erectile dysfunction among human immunodeficiency virus-infected men receiving testosterone and oxandrolone. J Sex Med, 2008;5(1):241-7.

8. Paulo LG, Fink GD, Roh BL, Fisher JW. Effects of several androgens and steroid metabolites on erythropoietin production in the isolated perfused dog kidney. Blood, 1974;43(1):39-47.

9. Alexanian R. Erythropoietin and erythropoiesis in anemic man following androgens. Blood, 1969;33(4):564-72.

Adapted with permission from Seth Robert’s Anabolic Pharmacology, all rights reserved.

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