Florina G

Levonorgestrel is a synthetic progestin hormone, the active levorotatory enantiomer of the racemic mixture norgestrel, structurally analogous to progesterone and used primarily in contraception.[1][2] It is administered orally as a single 1.5 mg dose for emergency contraception to prevent pregnancy following unprotected intercourse or contraceptive failure, with optimal efficacy when taken as soon as possible, up to 72 hours post-exposure.[3][4] Levonorgestrel also features in long-acting reversible contraception via intrauterine systems that release the hormone locally to inhibit ovulation, thicken cervical mucus, and thin the endometrial lining, providing up to five years of protection.[5] Its primary mechanism involves suppressing gonadotropin release to delay or prevent ovulation, though post-ovulatory effects on fertilization or implantation remain debated in empirical studies.[6][7] While generally safe and effective, reduced efficacy has been observed in individuals with higher body mass index, prompting recommendations for alternative methods like ulipristal acetate in such cases, based on pharmacokinetic data rather than direct causal trials.[8]