Levonorgestrel

Levonorgestrel is a synthetic progestin used in a variety of hormonal contraceptives and in products for reproductive health. It is the active pharmaceutical ingredient in many combined oral contraceptives, in some progestin-containing regimens designed for emergency contraception, and in intrauterine devices that release the hormone locally.

The primary mechanism of action of levonorgestrel depends on the method of use. In combination oral contraceptives, it suppresses ovulation, alters cervical mucus to impede sperm passage, and changes the endometrium to reduce the likelihood of implantation. In levonorgestrel-releasing intrauterine systems, the hormone acts mainly within the uterus to provide long-acting contraception and to lessen menstrual blood loss in some users.

Common medical uses include the prevention of pregnancy through combined oral contraceptives, emergency contraception after unprotected intercourse or a contraceptive failure, and long-acting reversible contraception with levonorgestrel-releasing intrauterine devices. Emergency contraception regimens typically aim to prevent pregnancy when taken within a few days after unprotected sex; LNG-based regimens do not protect against sexually transmitted infections.

Pharmacokinetically, levonorgestrel is absorbed after oral administration and undergoes metabolism in the liver, with elimination via urine and feces. The intrauterine system delivers the hormone locally, providing sustained release with systemic exposure that is lower than that from oral use.

Safety and side effects commonly include nausea, abdominal or pelvic discomfort, irregular vaginal bleeding, headaches, and breast tenderness. Contraindications include pregnancy, history of thrombosis or thromboembolic disease, active liver disease or liver tumors, undiagnosed vaginal bleeding, and certain types of hormone-sensitive cancers. Caution is advised in smokers over age 35 and in individuals taking drugs that induce liver enzymes. As with all hormonal contraception, levonorgestrel should be used under medical guidance, with consideration of individual health history and risk factors.