There is no age, I.D, or prescription required to purchase emergency contraception. Plan B hit the market in 1999 where it could be bought by anyone older than 18. However, in 2013, the rules were changed so that Plan B could be purchased at any age without ID or prescription. The primary mechanism of action of levonorgestrel as a progestogen-only emergency contraceptive pill is, according to International Federation of Gynecology and Obstetrics (FIGO), to prevent fertilization by inhibition of ovulation and thickening of cervical mucus. FIGO has stated that: "review of the evidence suggests that LNG [levonorgestreol] ECPs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling." In November 2013, the European Medicines Agency (EMA) approved a change to the label saying it cannot prevent implantation of a fertilized egg.Other studies still find the evidence to be unclear. While it is unlikely that emergency contraception affects implantation it is impossible to completely exclude the possibility of post-fertilization effect.In November 2013, the EMA also approved a change to the label for HRA Pharmas NorLevo saying: "In clinical trials, contraceptive efficacy was reduced in women weighing 75 kg [165 pounds] or more, and levonorgestrel was not effective in women who weighed more than 80 kg [176 pounds]."
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.