Pharmacodynamics As an AAS,<unk>  is an agonist of the androgen receptor (AR), similarly to androgens like testosterone and dihydrotestosterone (DHT).<unk>  is not a substrate for 5α-reductase and hence is not potentiated or inactivated in so-called "androgenic" tissues like the skin, hair follicles, and prostate gland. As such, it has a high ratio of anabolic to androgenic activity, similarly to other nandrolone derivatives.<unk>  is a substrate for aromatase and hence produces the estrogen 7α-methylestradiol as a metabolite. However,<unk>  has only weak estrogenic activity and an amount that would appear to be insufficient for replacement purposes, as evidenced by decreased bone mineral density in men treated with it for hypogonadism.<unk>  also has potent progestogenic activity. Both the androgenic and progestogenic activity of<unk>  are thought to be involved in its antigonadotropic activity. Relative affinities (%) of<unk>  and related steroids Compound Nandrolone 20 154–155 <0.1 0.5 1.6 1 ?<unk>  50–75 100–125 ? <1 ? ? ? 7α-Methylestradiol 1–3 15–25 101 <1 <1 ? ? Values are percentages (%). Reference ligands (100%) were progesterone for the , testosterone for the , for the , for the , aldosterone for the , for , and cortisol for . Mechanism of action Spermatozoa are produced in the testes of males in a process called spermatogenesis. In order to render a man infertile, a hormone-based male contraceptive method must stop spermatogenesis by interrupting the release of gonadotropins from the pituitary gland. Even in low concentrations,<unk>  is a potent inhibitor of the release of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). In order for spermatogenesis to occur in the testes, both FSH and testosterone must be present. By inhibiting release of FSH,<unk>  creates an endocrine environment in which conditions for spermatogenesis are not ideal. Manufacture of sperm is further impaired by the suppression of LH, which in turn drastically curtails the production of testosterone. Sufficient regular doses of<unk>  cause severe oligozoospermia or azoospermia, and therefore infertility, in most men.<unk> -induced infertility has been found to be quickly reversible upon discontinuation. When LH release is inhibited, the amount of testosterone made in the testes declines dramatically. As a result of<unk> 's gonadotropin-suppressing qualities, levels of serum testosterone fall sharply in men treated with sufficient amounts of the medication. Testosterone is the main hormone responsible for maintenance of male secondary sex characteristics. Normally, inadequate testosterone levels cause undesirable effects, such as fatigue, loss of skeletal muscle mass, reduced libido, and weight gain. However, the androgenic and anabolic properties of<unk>  largely ameliorate this problem. Essentially,<unk>  replaces testosterone's role as the primary male hormone in the body. Pharmacokinetics The pharmacokinetic properties of<unk> , such as poor oral bioavailability and short elimination half-life, make it unsuitable for oral administration or long-term intramuscular injection. As such,<unk>  must be administered parenterally via a different and more practical route such as subcutaneous implant, transdermal patch, or topical gel.<unk>  acetate, a prodrug of<unk> , can be administered via intramuscular injection.
Trestolone
Metenolone
Metenolone acetate
Fluocinonide
Trenbolone acetate
Oxymetholone
Methylstenbolone
Pregnenolone 