Etonogestrel has about 150% of the affinity of promegestone and 300% of the affinity of progesterone for the PR. Desogestrel (via etonogestrel) is a very potent progestogen and inhibits ovulation at very low doses, in the low microgram range. The effective minimum dosage for inhibition of ovulation is 60 μg/day desogestrel (alone, not in combination with an estrogen). However, some studies in combination with oral estradiol have suggested that higher doses may be necessary. Desogestrel and etonogestrel are among the most potent progestogens available, along with gestodene and levonorgestrel (which have effective ovulation-inhibiting dosages 40 μg/day and 60 μg/day, respectively). Oral desogestrel is clinically on the order of 5,000 times more potent than oral micronized progesterone (which has an effective ovulation-inhibiting dosage of more than 300 mg/day) in humans. Due to its progestogenic activity, desogestrel has potent functional antiestrogenic effects in certain tissues. It dose-dependently antagonizes the effects of ethinylestradiol on the vaginal epithelium, cervical mucus, and endometrium, with marked progestogenic effects occurring at a dosage of 60 μg/day. There is a rise in body temperature in some women at 30 μg/day and in all women at 60 μg/day. Desogestrel also has antigonadotropic effects, which are similarly due to its progestogenic activity. The contraceptive effects of desogestrel in women are mediated not only by prevention of ovulation via its antigonadotropic effects but also by its marked progestogenic and antiestrogenic effects on cervical mucus and the endometrium. Aside from its progestogenic activity, desogestrel also has some off-target hormonal activity at other steroid hormone receptors (see below). However, these activities are relatively weak, and desogestrel is said to be one of the most selective and pure progestogens used in oral contraceptives. Antigonadotropic effects Desogestrel has antigonadotropic effects via its progestogenic activity, similarly to other progestogens. It has been found to reduce testosterone levels by 15% in women at a dosage of 125 μg/day. In addition, desogestrel has been extensively investigated as an antigonadotropin at dosages of 150 to 300 μg/day in combination with testosterone in male contraceptive regimens. One study found that 150 μg/day and 300 μg/day desogestrel alone in healthy young men suppressed luteinizing hormone (LH) levels by about 35% and 42%, respectively; follicle-stimulating hormone (FSH) levels by about 47% and 55%, respectively; and testosterone levels by about 59% and 68%, respectively. LH levels were suppressed maximally by desogestrel within 3 days, whereas 14 days were necessary for maximal suppression of