As a contraceptive, it works primarily by preventing ovulation and closing off the cervix to prevent the passage of sperm. The endometrial transformation dose of levonorgestrel is 150 to 250 μg/day or 2.5 to 6 mg per cycle.Due to its progestogenic activity, levonorgestrel has antigonadotropic effects and is able to suppress the secretion of the gonadotropins, luteinizing hormone and follicle-stimulating hormone, from the pituitary gland. This in turn, results in suppression of gonadal activity, including reduction of fertility and gonadal sex hormone production in both women and men. The ovulation-inhibiting dose of levonorgestrel in premenopausal women is 50 to 60 μg/day.In men, levonorgestrel causes marked suppression of circulating testosterone levels secondary to its antigonadotropic effects. In healthy young men, levonorgestrel alone at a dose of 120 to 240 μg/day orally for 2 weeks suppressed testosterone levels from ~450 ng/dL to ~248 ng/dL (–45%). Because of its effects on testosterone levels, and due to its androgenic activity being only weak and hence insufficient for purposes of androgen replacement in males, levonorgestrel has potent functional antiandrogenic effects in men. Consequently, it is able to produce adverse effects like decreased libido and erectile dysfunction, among others. In relation to this, levonorgestrel has been combined with an androgen like testosterone or dihydrotestosterone when it has been studied as a hormonal contraceptive in men. Androgenic activity
Levonorgestrel is a weak agonist of the androgen receptor (AR), the main biological target of the androgen sex hormone testosterone.
Levonorgestrel is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand name Plan B among others, it is useful within 72 hours of unprotected sex. The more time that has passed since sex, the less effective the medication becomes, and it does not work after pregnancy (implantation) has occurred. Levonorgestrel works by preventing ovulation or fertilization from occurring. It decreases the chances of pregnancy by 57 to 93%. In an intrauterine device (IUD), such as Mirena among others, it is effective for the long-term prevention of pregnancy. A levonorgestrel-releasing implant is also available in some countries.Common side effects include nausea, breast tenderness, headaches, and increased, decreased, or irregular menstrual bleeding. When used as an emergency contraceptive, if pregnancy occurs, there is no evidence that its use harms the fetus. It is safe to use during breastfeeding. Birth control that contains levonorgestrel will not change the risk of sexually transmitted infections. It is a progestin and has effects similar to those of the hormone progesterone. It works primarily by preventing ovulation and closing off the cervix to prevent the passage of sperm.Levonorgestrel was patented in 1960 and introduced for medical use together with ethinylestradiol in 1970. It is on the World Health Organizations List of Essential Medicines. It is available as a generic medication. In the United States, levonorgestrel-containing emergency contraceptives are available over the counter (OTC) for all ages.