Mesterolone is a simple derivative of dihydrotestosterone and is commonly known by its trade name, Proviron. The addition of a methyl group to the 1 position, like methenolone, should help to provide a small amount of protection from metabolism when taken orally. In fact the only difference between methenolone and mesterolone is the presence of a double bond in the 1,2 position with methenolone.
This double bond changes the shape of the A-ring as well as the location of the 1-methyl group. Though these drugs are so similar in appearance, they are quite different in activity. While the 1-methyl and 1-double bond help to keep methenolone from being metabolized to inactive metabolites, the presence of only a 1 methyl group seems to provide mesterolone with little protection and it is likely deactivated quickly.
Since mesterolone is already 5-alpha reduced, it is not subject to further metabolism by 5-alpha reductase. Mesterolone, as a DHT-derivative, cannot be converted by aromatase to estrogenic metabolites and has some degree of inhibition of aromatase and likely some inhibition of 5-alpha reductase as well. In fact, many consider mesterolone to be an anti-estrogen, and its use in the literature seems to support this to some degree. Mesterolone is one of the strongest binder of SHBG commercially available, in fact, only DHT binds to SHBG more strongly1,2.
As discussed earlier, SHBG plays a very important role in testosterone metabolism. Because mesterolone binds so strongly to SHBG it tends to bump other less strongly bound molecules in the “free” state where they can bind the androgen receptor3. Therefore, some athletes have attempted to use mesterolone for this purpose. They add mesterolone to a cycle if the hopes that more steroid will remain free and active. This would also be true for testosterone and estrogen. Mesterolone would be capable of bumping both of these hormones into circulation as well which may result in androgenic or estrogenic effects.
There is no evidence that mesterolone binds to glucocorticoid or progesterone receptors. Mesterolone is not known for being very anabolic even though the anabolic to androgenic ratio when given subcutaneously is favorable. When given orally, mesterolone undergoes significant metabolism that greatly reduces any anabolic effect4.
The fact that mesterolone has been shown to have little effect on red blood cell production, unlike other androgens, seems to confirm its rapid metabolism5. Mesterolone has been studied quite extensively in the literature as a fertility treatment to increase sperm quantity. There is quite a bit of conflicting data showing mesterolone to have variable effects on LH and FSH, though it is generally been shown to not reduce normal levels of LH and FSH6. Though its use as an SHBG binder is somewhat questionable, it may have use in blocking the metabolism of other DHT derivatives by 3-alpha hydroxysteroid dehydrogenase since it seems to have significant affinity for this enzyme.
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. Jun;114(6):2100-6, 1984
2. 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. Jul;53(1):69-75, 1981
3. Aakvaag A, Stromme SB: The effect of mesterolone administration to normal men on the pituitary-testicular function. Acta Endocrinol (Copenh). Oct;77(2):380-6, 1974
4. Schanzer W: Metabolism of anabolic androgenic steroids. Clin Chem. Jul;42(7):1001-20, 1996
5. Jockenhövel F, Vogel E, Reinhardt W, Reinwein D. Effects of various modes of androgen substitution therapy on erythropoiesis. Eur J Med Res. 2(7):293-8, 1997
6. Varma TR, Patel RH. The effect of mesterolone on sperm count, on serum follicle stimulating hormone, luteinizing hormone, plasma testosterone and outcome in idiopathic oligospermic men. Int J Gynaecol Obstet. 26(1):121-8, 1988
Adapted with permission from Seth Robert’s Anabolic Pharmacology, all rights reserved.