FSH and testosterone levels. A previous study by the same authors found that increasing the dosage of desogestrel from 300 μg/day to 450 μg/day resulted in no further suppression of gonadotropin concentrations. The addition of a low dose of 50 or 100 mg/week intramuscular testosterone enanthate after 3 weeks increased testosterone levels and further suppressed LH and FSH levels, to the limits of assay detection (i.e., to undetectable or near-undetectable levels), in both the 150 μg/day and 300 μg/day desogestrel groups. Upon cessation of treatment, levels of LH, FSH, and testosterone all recovered to baseline values within 4 weeks. Androgenic activity Etonogestrel has about 20% of the affinity of metribolone and 50% of the affinity of levonorgestrel for the androgen receptor (AR) while desogestrel has no affinity for this receptor. The 5α-reduced metabolite of etonogestrel, 5α-dihydroetonogestrel (3-keto-5α-dihydrodesogestrel), also has some affinity for the AR (about 17% of that of metribolone). Desogestrel (via etonogestrel) has very low androgenic potency, about 1.9 to 7.4% of that of methyltestosterone in animal assays, and hence is considered to be a very weak androgen. Although etonogestrel has about the same affinity for the AR as norethisterone, due to the relatively increased progestogenic potency and decreased androgenic activity of etonogestrel, the drug has markedly higher selectivity for the PR over the AR than older 19-nortestosterone progestins like norethisterone and levonorgestrel. Conversely, its selectivity for the PR over the AR is similar to other newer 19-nortestosterone progestins like gestodene and norgestimate. It has been estimated that 150 μg/day desogestrel has less than one-sixth of the androgenic effect of 1 mg/day norethisterone (these being common dosages of the drugs used in combined oral contraceptives). Clinical studies with norethisterone even at very high dosages (e.g., 10 to 60 mg/day) have observed only mild androgenic effects in a minority of women including acne, increased sebum production, hirsutism, and slight virilization of female fetuses. In accordance with its very weak androgenic activity, desogestrel has minimal effects on lipid metabolism and the blood lipid profile, although there may still be some significant changes. Desogestrel also reduces sex hormone-binding globulin (SHBG) levels by 50% when given to women alone, but when combined with 30 μg/day ethinylestradiol, which in contrast strongly activates SHBG production, there is a 200% increase in SHBG concentrations. Desogestrel may slightly reduce ethinylestradiol-induced increases in SHBG levels. However, at the dosages used in oral contraceptives and in combination with ethinylestradiol,