Norethisterone

Norethisterone, also known as norethindrone and sold under many brand names, is a progestin medication used in birth control pills, menopausal hormone therapy, and for the treatment of gynecological disorders. The medication is available in both low-dose and high-dose formulations and both alone and in combination with an estrogen. It is used by mouth or, as norethisterone enanthate, by injection into muscle.

Norethisterone
Clinical data
Trade namesMany
Other namesNET; Norethindrone; NSC-9564; LG-202; Ethinylnortestosterone; Norpregneninolone; Anhydrohydroxy-norprogesterone; Ethinylestrenolone; 17α-Ethynyl-19-nortestosterone; 17α-Ethynylestra-4-en-17β-ol-3-one; 17α-Hydroxy-19-norpregn-4-en-20-yn-3-one
AHFS/Drugs.comMonograph
MedlinePlusa604034
License data
Routes of
administration		By mouth, intramuscular injection (as NETETooltip norethisterone enanthate)
Drug classProgestogen (medication); Progestin
ATC code
Legal status
Legal status
Pharmacokinetic data
Bioavailability47–73% (mean 64%)
Protein binding97%:
Albumin: 61%;
SHBGTooltip Sex hormone-binding globulin: 36%
MetabolismMainly CYP3A4 (liver); also 5α-/5β-reductase, 3α-Tooltip 3α-hydroxysteroid dehydrogenase/3β-HSDTooltip 3β-hydroxysteroid dehydrogenase, and aromatase
Elimination half-life5.2–12.8 hours (mean 8.0 hours)
Identifiers
  • (8R,9S,10R,13S,14S,17R)-17-ethynyl-17-hydroxy-13-methyl-1,2,6,7,8,9,10,11,12,14,15,16-dodecahydrocyclopenta[a]phenanthren-3-one
CAS Number
PubChem CID
IUPHAR/BPS
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
CompTox Dashboard (EPA)
ECHA InfoCard100.000.619
Chemical and physical data
FormulaC20H26O2
Molar mass298.426 g·mol−1
3D model (JSmol)
Melting point203 to 204 °C (397 to 399 °F)
  • C[C@]12CC[C@H]3[C@H]([C@@H]1CC[C@]2(C#C)O)CCC4=CC(=O)CC[C@H]34
  • InChI=1S/C20H26O2/c1-3-20(22)11-9-18-17-6-4-13-12-14(21)5-7-15(13)16(17)8-10-19(18,20)2/h1,12,15-18,22H,4-11H2,2H3/t15-,16+,17+,18-,19-,20-/m0/s1 Y
  • Key:VIKNJXKGJWUCNN-XGXHKTLJSA-N Y
  (verify)

Side effects of norethisterone include menstrual irregularities, headaches, nausea, breast tenderness, mood changes, acne, increased hair growth. Norethisterone is a progestin, or a synthetic progestogen, and hence is an agonist of the progesterone receptor, the biological target of progestogens like progesterone. It has weak androgenic and estrogenic activity, mostly at high dosages, and no other important hormonal activity.

Norethisterone was discovered in 1951 and was one of the first progestins to be developed. It was first introduced for medical use on its own in 1957 and was introduced in combination with an estrogen for use as a birth control pill in 1963. It is sometimes referred to as a "first-generation" progestin. Along with desogestrel, it is one of the only progestins that is widely available as a progestogen-only "mini pill" for birth control. Norethisterone is marketed widely throughout the world. It is available as a generic medication. In 2021, it was the 140th most commonly prescribed medication in the United States, with more than 4 million prescriptions. It is on the World Health Organization's List of Essential Medicines.

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