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2D Structure
Also known as: Norethisterone, 68-22-4, Micronor, Norethisteron, 19-norethisterone, Norlutin
Molecular Formula
C20H26O2
Molecular Weight
298.4  g/mol
InChI Key
VIKNJXKGJWUCNN-XGXHKTLJSA-N
FDA UNII
T18F433X4S

A synthetic progestational hormone with actions similar to those of PROGESTERONE but functioning as a more potent inhibitor of ovulation. It has weak estrogenic and androgenic properties. The hormone has been used in treating amenorrhea, functional uterine bleeding, endometriosis, and for contraception.
Norethindrone is a Progestin.
1 2D Structure

2D Structure

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
(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
2.1.2 InChI
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
2.1.3 InChI Key
VIKNJXKGJWUCNN-XGXHKTLJSA-N
2.1.4 Canonical SMILES
CC12CCC3C(C1CCC2(C#C)O)CCC4=CC(=O)CCC34
2.1.5 Isomeric SMILES
C[C@]12CC[C@H]3[C@H]([C@@H]1CC[C@]2(C#C)O)CCC4=CC(=O)CC[C@H]34
2.2 Other Identifiers
2.2.1 UNII
T18F433X4S
2.3 Synonyms
2.3.1 MeSH Synonyms

1. 19-norpregn-4-en-20-yn-3-one, 17-hydroxy-, (17alpha)-

2. Conceplan

3. Ethinylnortestosterone

4. Micronor

5. Monogest

6. Nor Qd

7. Nor-qd

8. Norcolut

9. Norcolute

10. Norethindrone, (1 Beta)-isomer

11. Norethisterone

12. Norlutin

13. Norpregneninolone

14. Norqd

2.3.2 Depositor-Supplied Synonyms

1. Norethisterone

2. 68-22-4

3. Micronor

4. Norethisteron

5. 19-norethisterone

6. Norlutin

7. Anovule

8. Gestest

9. Norcolut

10. Noriday

11. Utovlan

12. Camila

13. Primolut-n

14. Norethynodrone

15. Conludag

16. Micronovum

17. Norluten

18. Triella

19. Mini-pill

20. Nor-qd

21. Mini-pe

22. Noresthisterone

23. Norethisteronum

24. Conludaf

25. Micronett

26. Noralutin

27. Norethyndron

28. Norgestin

29. Norluton

30. Proluteasi

31. Norfor

32. Utovlar

33. Norpregneninlone

34. 19-nor-ethindrone

35. Ethinylnortestosterone

36. Noretisterona

37. 17alpha-ethynyl-19-nortestosterone

38. Ethynylnortestosterone

39. 19-nor-17alpha-ethynyltestosterone

40. Menzol

41. 17alpha-ethinyl-19-nortestosterone

42. Anhydrohydroxynorprogesterone

43. Minovlar

44. Nor-q.d.

45. 19-norethinyltestosterone

46. Norpregneninolone

47. Ethinyl-19-nortestosterone

48. Normapause

49. 17alpha-ethynyl-4-estren-17-ol-3-one

50. 17-alpha-ethynyl-19-nortestosterone

51. 19-nor-17-alpha-ethynyltestosterone

52. 19-norethindrone

53. 19-nor-17-ethinyltestosterone

54. 17alpha-ethinylestra-4-en-17beta-ol-3-one

55. 17beta-hydroxy-19-norpregn-4-en-20-yn-3-one

56. Nsc-9564

57. 17-alpha-ethynyl-4-estren-17-ol-3-one

58. 19-nor-17alpha-ethynyl-17beta-hydroxy-4-androsten-3-one

59. 17alpha-ethynyl-17-hydroxy-4-estren-3-one

60. Activella

61. 19-nor-17alpha-ethynylandrosten-17beta-ol-3-one

62. 4-estren-17alpha-ethynyl-17beta-ol-3-one

63. 17alpha-ethynyl-19-norandrost-4-en-17beta-ol-3-one

64. 17-hydroxy-19-nor-17alpha-pregn-4-en-20-yn-3-one

65. 17-alpha-ethynyl-17-hydroxy-4-estren-3-one

66. 17alpha-ethynyl-17beta-hydroxy-19-norandrost-4-en-3-one

67. 17-beta-hydroxy-19-norpregn-4-en-20-yn-3-one

68. Norethindrone (usp)

69. Norethindrone [usp]

70. Primolut N

71. Norethisterone [inn]

72. 19-nor-17-alpha-ethynylandrosten-17-beta-ol-3-one

73. 17-ethynyl-17beta-hydroxyestr-4-en-3-one

74. 17-alpha-ethynyl-19-norandrost-4-en-17-beta-ol-3-one

75. 17-hydroxy-19-nor-17-alpha-pregn-4-en-20-yn-3-one

76. Anovulatorio

77. Ciclovulan

78. Microneth

79. Norethadrone

80. Norethynodron

81. 19-nor-17-alpha-ethynyl-17-beta-hydroxy-4-androsten-3-one

82. Estrinor

83. Gencept

84. Norethin

85. Synphase

86. Genora

87. Milli

88. Nelova

89. Nodiol

90. Noraethisteronum

91. Norpregneninotone

92. Chembl1162

93. Combipatch

94. Norcept-e

95. 17alpha-ethynyl-19-nor-4-androsten-17beta-ol-3-one

96. Norethindrone (norethisterone)

97. Synphasic 28

98. (17-alpha)-17-hydroxy-19-norpregn-4-en-20-yn-3-one

99. Brevinor 21

100. Brevinor 28

101. Chebi:7627

102. Trinovum 21

103. Noriday 28

104. Errin

105. Jenest-28

106. Ethynylmortestosterone

107. Brevinor-1 21

108. Brevinor-1 28

109. T18f433x4s

110. Tri-norinyl

111. Ovysmen 1 35

112. Noretisterone [dcit]

113. Ortho-novum 1 35

114. Ortho-novum 1 50

115. Sc 4640

116. Ortho-novum 7 7 7

117. Ovysmen 0.5 35

118. Ortho 1 35

119. (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

120. Sc-4640

121. Ortho 7 7 7

122. Noretisterone

123. 19-nortestosterone, 17-ethynyl-

124. Norethisteronum [inn-latin]

125. Noretisterona [inn-spanish]

126. Dsstox_cid_3380

127. Dsstox_rid_77005

128. 17alpha-hydroxy-19-norpregn-4-en-20-yn-3-one

129. Dsstox_gsid_23380

130. Nora-be

131. Norethisterone [progestins]

132. (14beta,17alpha)-17-ethynyl-17-hydroxyestr-4-en-3-one

133. Norethindirone

134. 17-ethinyl-19-nortestosterone

135. (17alpha)-17-ethynyl-17-hydroxyestra-4,8(14),9-trien-3-one

136. 19-nor-17alpa-ethynyltestosterone

137. Micronor (tn)

138. (8r,9s,10r,13s,14s,17r)-17-ethynyl-17-hydroxy-13-methyl-1,2,6,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-3h-cyclopenta[a]phenanthren-3-one

139. Smr000499579

140. Ccris 484

141. Norethisterone (norethindrone)

142. Primolut-n (tn)

143. Camila (tn)

144. N.e.e.

145. 19-nor-17-ethinyl Testosterone

146. Hsdb 3370

147. 19-nor-ethinyl--4,5-testosterone

148. Einecs 200-681-6

149. Brn 1915671

150. 19-norpregn-4-en-20-yn-3-one, 17-hydroxy-, (17.alpha.)-

151. Heather Whole

152. Unii-t18f433x4s

153. Ai3-26422

154. 17-alpha-ethinylestra-4-en-17-beta-ol-3-one

155. Cas-68-22-4

156. Estr-4-en-3-one, 17alpha-ethynyl-17-hydroxy-

157. Ncgc00094738-01

158. Ent

159. Net

160. Prestwick_646

161. Calluna Vulgaris Whole

162. 17-alpha-19-norpregn-4-en-20-yn-3-one, 17-hydroxy-

163. 17alpha-ethinyl-17beta-hydroxy-delta(sup:4)-estren-3-one

164. 19-nor-17alpha-pregn-4-en-20-yn-3-one, 17-hydroxy-

165. 17-alpha-ethinyl-17-beta-hydroxy-delta(sup:4)-estren-3-one

166. 17-alpha-ethynyl-17-beta-hydroxy-19-norandrost-4-en-3-one

167. Norethisterone (jp17)

168. Prestwick0_000253

169. Prestwick1_000253

170. Prestwick2_000253

171. Prestwick3_000253

172. Norethindrone [mi]

173. 17-hydroxy-19-nor-17.alpha.-pregn-4-en-20-yn-3-one

174. Ec 200-681-6

175. Norethindrone [hsdb]

176. Norethisterone [jan]

177. Schembl23390

178. Bspbio_000066

179. Levonorgestrel Ep Impurity U

180. Norethindrone [vandf]

181. Mls001076679

182. Mls001163874

183. Norethisterone / Norethindrone

184. Spbio_002285

185. Norethindrone [usp-rs]

186. Norethisterone [mart.]

187. Bpbio1_000074

188. Gtpl2880

189. 17-ethynyl-19-nortestosterone

190. Norethisterone [who-dd]

191. Norethisterone [who-ip]

192. (17alpha)-17-hydroxy-19-norpregn-4-en-20-yn-3-one

193. Dtxsid9023380

194. 17-ethinyl-19-nor-testosterone

195. 19-nor-17-alpha-pregn-4-en-20-yn-3-one, 17-hydroxy-

196. Hms1568d08

197. Hms2090d21

198. Hms2095d08

199. Hms2231e18

200. Hms3259c16

201. Hms3712d08

202. Norethindrone [orange Book]

203. Bcp28306

204. Hy-b0554

205. 17alpha-pregn-4-en-20-yn-3-one

206. Norethindrone [usp Impurity]

207. Norethisterone [ep Impurity]

208. Tox21_111322

209. Tox21_302427

210. 19-norethindrone, >=98%, Powder

211. Bdbm50148732

212. Lmst02030097

213. Norethindrone [usp Monograph]

214. S4040

215. Zinc85205451

216. Norinyl Component Norethindrone

217. Vyfemla Component Norethindrone

218. Akos005267172

219. Aranelle Component Norethindrone

220. Brevicon Component Norethindrone

221. Norethisteronum [who-ip Latin]

222. Taytulla Component Norethindrone

223. Tox21_111322_1

224. Ccg-220253

225. Db00717

226. Nc00576

227. Femcon Fe Component Norethindrone

228. Ncgc00179669-01

229. Ncgc00179669-02

230. Ncgc00179669-04

231. Ncgc00255187-01

232. Ac-11100

233. Ac-33117

234. As-56451

235. Cpd000499579

236. Norethindrone Component Of Aranelle

237. Norquest Fe Component Norethindrone

238. 17alpha-ethynyl-17-hydroxyest-4-en-3-one

239. 17alpha-ethynyl-3-oxo-4-estren-17beta-ol

240. Norethindrone Component Of Femcon Fe

241. N0449

242. Norethindrone Component Of Norquest Fe

243. 17alpha-ethynyl-17-hydroxy-estr-4-en-3-one

244. Lo Minastrin Fe Component Norethindrone

245. Norethisterone 100 Microg/ml In Acetonitrile

246. C05028

247. C76161

248. D00182

249. Levonorgestrel Impurity U [ep Impurity]

250. Minastrin 24 Fe Component Norethindrone

251. 17alpha-ethynyl-17beta-hydroxyestr-4-en-3-one

252. 17beta-hydroxy-17alpha-ethynylestr-4-en-3-one

253. 067n596

254. 17-alpha-ethynyl-17-beta-hydroxy-4-estren-3-one

255. A836053

256. Q421352

257. Sr-01000765382

258. 17alpha-ethinyl-17alpha-ethinyl-19-nortestosterone

259. Sr-01000765382-3

260. W-104686

261. 13-methyl-17alpha-ethynyl-17-hydroxygon-4-en-3-one

262. 17-hydroxy-17-alpha-19-norpregn-4-en-20-yn-3-one

263. 17-hydroxy-19-nor-17alpha-pregn-4-en-20yn-3-one

264. 19-norethindrone, Vetranal(tm), Analytical Standard

265. Brd-k92073408-001-03-3

266. Brd-k92073408-001-16-5

267. Norethisterone Acetate Impurity A [ep Impurity]

268. 17-hydroxy-(17alpha)-19-norpregn-4-en-20-yn-3-one

269. 17-ethynyl-17-hydroxyestr-4-en-3-one (acd/name 4.0)

270. Norethisterone, British Pharmacopoeia (bp) Reference Standard

271. Norethisterone, European Pharmacopoeia (ep) Reference Standard

272. Norethindrone, United States Pharmacopeia (usp) Reference Standard

273. Norethisterone For System Suitability, European Pharmacopoeia (ep) Reference Standard

274. Norethindrone (norethisterone), Pharmaceutical Secondary Standard; Certified Reference Material

275. Norethisterone; 19-norethisterone; 17?-ethynyl-19-nortestosterone; 17-hydroxy-19-nor-17?-pregn-4-en-20-yn-3-one

2.4 Create Date
2005-06-24
3 Chemical and Physical Properties
Molecular Weight 298.4 g/mol
Molecular Formula C20H26O2
XLogP33
Hydrogen Bond Donor Count1
Hydrogen Bond Acceptor Count2
Rotatable Bond Count1
Exact Mass298.193280068 g/mol
Monoisotopic Mass298.193280068 g/mol
Topological Polar Surface Area37.3 Ų
Heavy Atom Count22
Formal Charge0
Complexity594
Isotope Atom Count0
Defined Atom Stereocenter Count6
Undefined Atom Stereocenter Count0
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Drug Information
1 of 12  
Drug NameActivella
PubMed HealthEstradiol/Norethindrone
Drug ClassesContraceptive, Estrogen/Progestin Combination, Monophasic Contraceptive Combination
Active Ingredientnorethindrone acetate; Estradiol
Dosage FormTablet
Routeoral; Oral
Strength0.5mg; 1mg; 1mg/0.5mg; 0.1mg
Market StatusPrescription
CompanyAmneal Pharms; Novo Nordisk

2 of 12  
Drug NameCamila
PubMed HealthNorethindrone (By mouth)
Drug ClassesContraceptive, Contraceptive, Progestin, Endocrine-Metabolic Agent
Drug LabelEach light pink Camila tablet provides a continuous oral contraceptive regimen of 0.35 mg norethindrone USP daily, and has the following inactive ingredients: corn starch, FD&C red no. 40 aluminum lake, lactose monohydrate, magnesium stearate, povi...
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyBarr

3 of 12  
Drug NameErrin
PubMed HealthNorethindrone (By mouth)
Drug ClassesContraceptive, Contraceptive, Progestin, Endocrine-Metabolic Agent
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyBarr

4 of 12  
Drug NameMicronor
PubMed HealthNorethindrone (By mouth)
Drug ClassesContraceptive, Contraceptive, Progestin, Endocrine-Metabolic Agent
Drug LabelEach tablet contains 0.35 mg norethindrone. Inactive ingredients include corn starch, D&C Green No. 5, D&C Yellow No. 10, lactose, magnesium stearate, and povidone....
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyJanssen Pharms

5 of 12  
Drug NameNorethindrone
Drug LabelEach light pink Camila tablet provides a continuous oral contraceptive regimen of 0.35 mg norethindrone USP daily, and has the following inactive ingredients: corn starch, FD&C red no. 40 aluminum lake, lactose monohydrate, magnesium stearate, povi...
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyNovast Labs; Lupin; Famy Care; Glenmark Generics; Haupt Pharma

6 of 12  
Drug NameNor-qd
Drug LabelEach yellow Nor-QD tablet provides a continuous oral contraceptive regimen of 0.35 mg norethindrone daily, and the inactive ingredients include D&C Yellow No. 10, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and starch.The chemical na
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyWatson Labs (utah)

7 of 12  
Drug NameActivella
PubMed HealthEstradiol/Norethindrone
Drug ClassesContraceptive, Estrogen/Progestin Combination, Monophasic Contraceptive Combination
Active Ingredientnorethindrone acetate; Estradiol
Dosage FormTablet
Routeoral; Oral
Strength0.5mg; 1mg; 1mg/0.5mg; 0.1mg
Market StatusPrescription
CompanyAmneal Pharms; Novo Nordisk

8 of 12  
Drug NameCamila
PubMed HealthNorethindrone (By mouth)
Drug ClassesContraceptive, Contraceptive, Progestin, Endocrine-Metabolic Agent
Drug LabelEach light pink Camila tablet provides a continuous oral contraceptive regimen of 0.35 mg norethindrone USP daily, and has the following inactive ingredients: corn starch, FD&C red no. 40 aluminum lake, lactose monohydrate, magnesium stearate, povi...
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyBarr

9 of 12  
Drug NameErrin
PubMed HealthNorethindrone (By mouth)
Drug ClassesContraceptive, Contraceptive, Progestin, Endocrine-Metabolic Agent
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyBarr

10 of 12  
Drug NameMicronor
PubMed HealthNorethindrone (By mouth)
Drug ClassesContraceptive, Contraceptive, Progestin, Endocrine-Metabolic Agent
Drug LabelEach tablet contains 0.35 mg norethindrone. Inactive ingredients include corn starch, D&C Green No. 5, D&C Yellow No. 10, lactose, magnesium stearate, and povidone....
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyJanssen Pharms

11 of 12  
Drug NameNorethindrone
Drug LabelEach light pink Camila tablet provides a continuous oral contraceptive regimen of 0.35 mg norethindrone USP daily, and has the following inactive ingredients: corn starch, FD&C red no. 40 aluminum lake, lactose monohydrate, magnesium stearate, povi...
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyNovast Labs; Lupin; Famy Care; Glenmark Generics; Haupt Pharma

12 of 12  
Drug NameNor-qd
Drug LabelEach yellow Nor-QD tablet provides a continuous oral contraceptive regimen of 0.35 mg norethindrone daily, and the inactive ingredients include D&C Yellow No. 10, FD&C Yellow No. 6, lactose, magnesium stearate, povidone, and starch.The chemical na
Active IngredientNorethindrone
Dosage FormTablet
RouteOral-28
Strength0.35mg
Market StatusPrescription
CompanyWatson Labs (utah)

4.2 Therapeutic Uses

Contraceptives, Oral, Synthetic; Progestational Hormones, Synthetic

National Library of Medicine's Medical Subject Headings online file (MeSH, 2009)


AYGESTIN is indicated for the treatment of secondary amenorrhea, endometriosis, and abnormal uterine bleeding due to hormonal imbalance in the absence of organic pathology, such as submucous fibroids or uterine cancer. AYGESTIN is not intended, recommended or approved to be used with concomitant estrogen therapy in postmenopausal women for endometrial protection. /Included in US product label/

US Natl Inst Health; DailyMed. Current Medication Information for AYGESTIN (norethindrone acetate) tablet (July 2007). Available from, as of February 14, 2010: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=21992


Oral contraceptives are indicated for the prevention of pregnancy in women who elect to use this product as a method of contraception. /Included in US product label/

US Natl Inst Health; DailyMed. Current Medication Information for BALZIVA (norethindrone and ethyl estradiol) kit (September 2009). Available from, as of February 28, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=11472


Progestin-only oral contraceptives are indicated for the prevention of pregnancy. /Included in US product label/

US Natl Inst Health; DailyMed. Current Medication Information for CAMILA (norethindrone) tablet (January 2011). Available from, as of February 28, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=37602


For more Therapeutic Uses (Complete) data for NORETHINDRONE (6 total), please visit the HSDB record page.


4.3 Drug Warning

VET: MARKED RAT, MONKEY, & DOG FETAL MASCULINIZATION HAS BEEN OBSERVED AS IN HUMAN. EXCESSIVE DOSAGE DURING PREGNANCY MAY ALSO CAUSE FETAL DEATH, TERATOGENICITY, & DELAYED PARTURITION.

Rossoff, I.S. Handbook of Veterinary Drugs. New York: Springer Publishing Company, 1974., p. 394


Cigarette smoking increases the risk of serious cardiovascular side effects from oral contraceptive use. This risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over 35 years of age. Women who use oral contraceptives should be strongly advised not to smoke.

US Natl Inst Health; DailyMed. Current Medication Information for BALZIVA (norethindrone and ethyl estradiol) kit (September 2009). Available from, as of February 28, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=11472


Norethindrone, like other progestins, may cause breakthrough bleeding, spotting, changes in menstrual flow, amenorrhea, changes in cervical erosion and secretions, edema, weight gain or loss, cholestatic jaundice, allergic rash with or without pruritus, melasma or chloasma, and mental depression.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 3278


When breakthrough bleeding or irregular vaginal bleeding occurs during norethindrone therapy, nonfunctional causes should be considered. Adequate diagnostic procedures should be performed in patients with undiagnosed vaginal bleeding.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 3278


For more Drug Warnings (Complete) data for NORETHINDRONE (44 total), please visit the HSDB record page.


4.4 Minimum/Potential Fatal Human Dose

3(?). 3= MODERATELY TOXIC: PROBABLE ORAL LETHAL DOSE (HUMAN) 0.5-5 G/KG, BETWEEN 1 OZ & 1 PINT FOR 70 KG PERSON (150 LB). /NORETHINDRONE WITH MESTRANOL/

Gosselin, R.E., H.C. Hodge, R.P. Smith, and M.N. Gleason. Clinical Toxicology of Commercial Products. 4th ed. Baltimore: Williams and Wilkins, 1976., p. II-174


4.5 Drug Indication

Norethisterone is indicated as an oral contraceptive when given as monotherapy or in combination with an estrogen component, such as [ethinylestradiol] or [estradiol]. In combination with an estrogen component, oral norethisterone is also indicated as a hormone replacement therapy in the treatment of postmenopausal osteoporosis and moderate-to-severe vasomotor symptoms arising from menopause. When applied via transdermal patch, the combination of norethisterone and estradiol is indicated for the treatment of hypoestrogenism, vulvovaginal atrophy, and moderate-severe vasomotor symptoms. Norethisterone, taken in combination with intramuscular [leuprolide], is also indicated for the symptomatic treatment of endometriosis-related pain.


5 Pharmacology and Biochemistry
5.1 Pharmacology

Norethisterone is a synthetic oral progestin used for contraception or to treat other hormone-related conditions such as menopausal symptoms and endometriosis. As a synthetic progestin, norethisterone acts similarly to endogenous progesterone but with a much higher potency - it acts at the pelvic level to alter cervical and endometrial function, as well as via the inhibition of pituitary hormones that play a role in follicular maturation and ovulation. A small increase in the risk of developing breast cancer has been observed in patients using combined oral contraceptives, with some evidence also implicating progestin-only pills - patients starting hormonal contraception should be advised of this risk and should employ routine breast self-examinations to check for evidence of any developing masses.


5.2 MeSH Pharmacological Classification

Contraceptives, Oral, Synthetic

Oral contraceptives which owe their effectiveness to synthetic preparations. (See all compounds classified as Contraceptives, Oral, Synthetic.)


Contraceptives, Oral, Hormonal

Oral contraceptives which owe their effectiveness to hormonal preparations. (See all compounds classified as Contraceptives, Oral, Hormonal.)


5.3 FDA Pharmacological Classification
5.3.1 Active Moiety
NORETHINDRONE
5.3.2 FDA UNII
T18F433X4S
5.3.3 Pharmacological Classes
Progestin [EPC]; Progesterone Congeners [CS]
5.4 ATC Code

G03FA01

S76 | LUXPHARMA | Pharmaceuticals Marketed in Luxembourg | Pharmaceuticals marketed in Luxembourg, as published by d'Gesondheetskeess (CNS, la caisse nationale de sante, www.cns.lu), mapped by name to structures using CompTox by R. Singh et al. (in prep.). List downloaded from https://cns.public.lu/en/legislations/textes-coordonnes/liste-med-comm.html. Dataset DOI:10.5281/zenodo.4587355


G - Genito urinary system and sex hormones

G03 - Sex hormones and modulators of the genital system

G03A - Hormonal contraceptives for systemic use

G03AC - Progestogens

G03AC01 - Norethisterone


G - Genito urinary system and sex hormones

G03 - Sex hormones and modulators of the genital system

G03D - Progestogens

G03DC - Estren derivatives

G03DC02 - Norethisterone


5.5 Absorption, Distribution and Excretion

Absorption

The Cmax of norethisterone following oral administration of a single dose ranges from 5.39 to 7.36 ng/mL with a Tmax of 1-2 hours. AUC0-24 values following single oral doses range from approximately 30 to 37 ng*hr/mL. The oral bioavailability of norethisterone is approximately 64%. When applied transdermally, norethisterone is well-absorbed through the skin, reaches steady-state concentrations within 24 hours, and has a Cmax ranging from 617 to 1060 pg/mL at steady state. Norethisterone is often formulated as norethisterone acetate, which is completely and rapidly deacetylated to norethisterone following oral administration - the disposition of norethisterone acetate is indistinguishable from that of orally administered norethisterone.


Route of Elimination

Following administration of radio-labeled norethisterone, slightly more than 50% of the administered dose was eliminated in the urine and 20-40% was eliminated in the feces.


Volume of Distribution

The volume of distribution of norethisterone is approximately 4 L/kg. Sulfated metabolites of norethisterone, as well as small quantities of parent drug, have been shown to distribute into breast milk.


Clearance

The plasma clearance of norethisterone has been estimated as 0.4 L/hr/kg, and the intrinsic clearance is approximately 73-81 L/h.


Norethindrone is 36% bound to sex hormone-binding globulin (SHBG) and 61% bound to albumin. Volume of distribution of norethindrone is about 4 L/kg.

US Natl Inst Health; DailyMed. Current Medication Information for AYGESTIN (norethindrone acetate) tablet (July 2007). Available from, as of February 14, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=21992


Plasma clearance value for norethindrone is approximately 0.4 L/hr/kg.

US Natl Inst Health; DailyMed. Current Medication Information for AYGESTIN (norethindrone acetate) tablet (July 2007). Available from, as of February 14, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=21992


In 25 BALB/c mice implanted subcutaneously with pellets containing 40% norethisterone and 60% cholesterol for 76-77 wk, absorption of norethisterone was estimated to be between 3.6 and 15.9 ug/day (mean, 7.7 ug/day).

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V21 452 (1979)


Rabbits excrete norethisterone metabolites predominantly in the urine ... while rats excrete them to 80% in bile ... .

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V21 453 (1979)


For more Absorption, Distribution and Excretion (Complete) data for NORETHINDRONE (8 total), please visit the HSDB record page.


5.6 Metabolism/Metabolites

Norethisterone is extensively metabolized, primarily in the liver, to a number of metabolites via partial and total reduction of its A-ring. The enzymes predominantly involved are 3- and 3-hydroxysteroid dehydrogenase (HSD) as well as 5- and 5-reductase. The 5-reduced metabolites, including 5-dihydronorethisterone and its derivatives, appear to carry biological activity while the 5-reduced metabolites appear inactive. Norethisterone and its metabolites are also extensively conjugated - most of the plasmatic metabolites are sulfate conjugates, while most of the urinary metabolites are glucuronide conjugates. The major metabolites in plasma are a disulfate conjugate of 3,5-tetrahydronorethisterone and a monosulfate conjugate of 3,5-tetrahydronorethisterone, while the major metabolite(s) in the urine are comprised of glucuronide and/or sulfate conjugates of 3,5-tetrahydronorethisterone. Norethisterone has also been observed to undergo some degree of metabolism via the cytochrome P450 enzyme system, predominantly by CYP3A4 and, to a much lesser extent, by CYP2C19, CYP1A2, and CYP2A6. The metabolites generated by these reactions have not been fully characterized.


Norethindrone undergoes extensive biotransformation, primarily via reduction, followed by sulfate and glucuronide conjugation. The majority of metabolites in the circulation are sulfates, with glucuronides accounting for most of the urinary metabolites.

US Natl Inst Health; DailyMed. Current Medication Information for AYGESTIN (norethindrone acetate) tablet (July 2007). Available from, as of February 14, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=21992


Norethisterone undergoes extensive ring A reduction to form dihydro- and tetrahydronorethisterone metabolites that undergo conjugation; it can also be aromatized. Low serum levels of ethinylestradiol have been measured in postmenopausal women following oral administration of relatively large doses of norethisterone acetate or norethisterone. On the basis of the area-under-the-curve (AUC) values that were determined for ethinylestradiol and norethisterone, it was shown that the mean conversion ratio of norethisterone to ethinylestradiol was 0.7 and 1.0% at doses of 5 and 10 mg, respectively. The authors calculated that this corresponds to an oral dose equivalent of about 6 ug ethinylestradiol/ mg of norethisterone acetate. Similarly, it was shown that a dose of 5 mg norethisterone administered orally was equivalent to about 4 ug ethinylestradiol/mg norethisterone.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V91 145 (2007)


After incubation of norethisterone with dog liver microsomes the 4beta,5beta-epoxide of norethisterone and a 6-oxygenated norethisterone derivative were obtained as minor metabolites ... .

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V21 453 (1979)


Rabbit liver homogenates ... catalyze the deethinylation of norethisterone, giving rise to the metabolite oestr-4-ene-3,17-dione.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V21 453 (1979)


For more Metabolism/Metabolites (Complete) data for NORETHINDRONE (7 total), please visit the HSDB record page.


Norethindrone has known human metabolites that include Norethindrone-O-glucuronide.

S73 | METXBIODB | Metabolite Reaction Database from BioTransformer | DOI:10.5281/zenodo.4056560


5.7 Biological Half-Life

The half-life of norethisterone has been variably estimated as 8-10 hours.


The mean terminal elimination half-life of norethindrone following a single dose administration of AYGESTIN is approximately 9 hours.

US Natl Inst Health; DailyMed. Current Medication Information for AYGESTIN (norethindrone acetate) tablet (July 2007). Available from, as of February 14, 2011: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=21992


The plasma half-life, MCR and plasma metabolite levels at various time intervals have been studied in six women after an intravenous injection of 3H-norethindrone acetate. The disappearance curve due to norethindrone acetate showed an initial rapid disappearance of 3H with an average half-life of 7.5 minutes and a subsequent slow disapperance with a half-life of 51.5 hours. Norethindrone acetate was cleared from the plasma with an average MCR of 495 L/day. Norethindrone acetate is rapidly metabolised after an intravenous injection. Norethindrone, the main metabolite, disappears from the plasma with an average half-life of 34.8 hours. Norethindrone maintains a high level compared with norethindrone acetate at all time intervals up to 24 hours and an equilibrium is reached between the two at 24 to 48 hours.

PMID:484634 Singh H et al; Am J Obstet Gynecol 135 (3): 409-14 (1979)


The half-life (of the beta phase of a two-component model) of elimination ranged from 4.8 to 12.8 hr (mean, 7.6 hr) with no significant differences between oral and intravenous administration.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V91 145 (2007)


5.8 Mechanism of Action

On a molecular level, progestins like norethisterone exert their effects on target cells via binding to progesterone receptors that result in downstream changes to target genes. Target cells are found in the reproductive tract, breast, pituitary, hypothalamus, skeletal tissue, and central nervous system. Contraceptive efficacy is derived mainly from changes to the cervical mucus, wherein norethisterone increases the cell content and viscosity of the mucous to impede sperm transport and migration. Norethisterone also induces a variety of changes to the endometrium - including atrophy, irregular secretion, and suppressed proliferation - that make it inhospitable for implantation. Working via a negative feedback loop, norethisterone also acts on both the hypothalamus and anterior pituitary to suppress the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. Suppression of these hormones prevents follicular development, ovulation, and corpus luteum development. When used as a component of hormone replacement therapy in menopausal women, norethisterones value is mainly in suppressing the growth of the endometrium. As estrogen stimulates endometrial growth, the unopposed use of estrogen in postmenopausal women with an intact uterus can lead to endometrial hyperplasia which can increase the risk of endometrial cancer. The addition of a progestin to a hormone replacement therapy in this population protects against this endometrial hyperplasia and, therefore, lowers the risk associated with the use of hormone replacement therapies. Norethisterone, along with other progestins and endogenous progesterone, has a low affinity for other steroid receptors, such as the androgen receptor and glucocorticoid receptor. While affinity and agonistic activity at these receptors is minimal, it is thought that androgen receptor agonism is responsible for some of the adverse effects observed with progestin use (e.g. acne, serum lipid changes).


Norethindrone shares the actions of progestins. Although the exact mechanism of action of progestin-only oral contraceptives is not known, norethindrone, when administered in usual contraceptive doses, appears to act principally by altering cervical mucus so that sperm migration into the uterus is inhibited. Progestational changes in the endometrium also occur which may inhibit implantation of the fertilized ovum in the uterus. In addition, continuous administration of low doses of norethindrone alters the rate of ovum transport by changing motility and secretion in fallopian tubes. Norethindrone prevents pregnancy even in the presence of ovulation. Norethindrone suppresses ovulation and causes ovarian and endometrial atrophy at high doses; the drug does not consistently suppress ovulation when administered in a continuous low-dose regimen. In low doses, norethindrone causes variable suppression of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Norethindrone has mild androgenic activity. At low doses, norethindrone also has some estrogenic activity.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 3119


Norethindrone shares the pharmacologic actions of the progestins. In women with adequate endogenous estrogen, norethindrone transforms a proliferative endometrium into a secretory one. Norethindrone has been shown to have some estrogenic, androgenic, and anabolic activity. The drug inhibits the secretion of pituitary gonadotropins at usual dosages and thus prevents follicular maturation and ovulation.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 3279


Progestins enter target cells by passive diffusion and bind to cytosolic (soluble) receptors that are loosely bound in the nucleus. The steroid receptor complex initiates transcription, resulting in an increase in protein synthesis. /Progestins/

USP. Convention. USPDI - Drug Information for the Health Care Professional. 20th ed. Volume I. Micromedex, Inc. Englewood, CO., 2000. Content Reviewed and Approved by the U.S. Pharmacopeial Convention, Inc., p. 2568


Progestins are capable of affecting serum concentrations of other hormones, particularly estrogen. Estrogenic effects are modified by the progestins, either by reducing the availability or stability of the hormone receptor complex or by turning off specific hormone-responsive genes by direct interaction with the progestin receptor in the nucleus. In addition, estrogen priming is necessary to increase progestin effects by upregulating the number of progestin receptors and/or increasing progesterone production, causing a negative feedback mechanism that inhibits estrogen receptors. /Progestins/

USP. Convention. USPDI - Drug Information for the Health Care Professional. 20th ed. Volume I. Micromedex, Inc. Englewood, CO., 2000. Content Reviewed and Approved by the U.S. Pharmacopeial Convention, Inc., p. 2568


For more Mechanism of Action (Complete) data for NORETHINDRONE (9 total), please visit the HSDB record page.