Levonorgestrel is a hormonal medication which is used in a number of birth control methods.In pill form, sold under the brand name Plan B among others, it is useful within 120 hours as emergency birth control.It becomes less effective the longer after sex and only works before pregnancy has occurred.It is also combined with an estrogen to make combined oral birth control pills.Within an intrauterine device (IUD), sold as Mirena among others, it is effective for long-term prevention of pregnancy.An implantable form of levonorgestrel is also available in some countries.
Common side effects include nausea, breast tenderness, headaches, and increased, decreased, or irregular menstrual bleeding.When used as a form of emergency contraception, if pregnancy occurs, there is no evidence its use harms the baby.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 mostly by preventing ovulation and closing off the cervix to prevent the passage of sperm.
Levonorgestrel was first made in the 1960s and its use as a method of birth control began in the 1980s.It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system.It is available as a generic medication.
At low doses, levonorgestrel is used in monophasic and triphasic formulations of combined oral contraceptive pills, with available monophasic doses ranging from 100–250 µg, and triphasic doses of 50 µg/75 µg/125 µg. It is combined with the estrogen ethinylestradiol in these formulations.
At very low daily dose of 30 µg, levonorgestrel is used in some progestogen only pill formulations.
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| Clinical data | |
|---|---|
| Trade names | Plan B, others |
| Synonyms | LNG; L-Norgestrel; WY-5104; 18-Methylnorethisterone; 17α-Ethynyl-18-methyl-19-nortestosterone; 17α-Ethynyl-18-methylestr-4-en-17β-ol-3-one; 13β-Ethyl-17α-hydroxy-18,19-dinorpregn-4-en-20-yn-3-one |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a610021 |
| Pregnancy category |
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| Routes of administration | By mouth, implant, insert (extended-release) |
| Drug class | Progestin; Progestogen |
| ATC code | |
| Legal status | |
| Legal status |
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| Pharmacokinetic data | |
| Bioavailability | ~100% |
| Protein binding | 55% |
| Metabolism | Liver via CYP3A4[citation needed] |
| Biological half-life | 36 ± 13 hours |
| Excretion | Kidney: 45% Feces: 32% |
| Chemical and physical data | |
|---|---|
| Formula | C21H28O2 |
| Molar mass | 312.446 g/mol |
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