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Mestranol molecule ball.png
Clinical data
Trade namesEnovid, Norinyl, Ortho-Novum, others
Other namesEthinylestradiol 3-methyl ether; EEME; EE3ME; CB-8027; L-33355; RS-1044; 17α-Ethynylestradiol 3-methyl ether; 17α-Ethynyl-3-methoxyestra-1,3,5(10)-trien-17β-ol; 3-Methoxy-19-norpregna-1,3,5(10)-trien-20-yn-17β-ol
AHFS/Drugs.comInternational Drug Names
Routes of
By mouth[1]
Drug classEstrogen; Estrogen ether
ATC code
  • None
Legal status
Legal status
  • In general: ℞ (Prescription only)
Pharmacokinetic data
Elimination half-lifeMestranol: 50 min[2]
EE: 7–36 hours[3][4][5][6]
  • (8R,9S,13S,14S,17R)-17-ethynyl-3-methoxy-13-methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthren-17-ol
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard100.000.707 Edit this at Wikidata
Chemical and physical data
Molar mass310.437 g·mol−1
3D model (JSmol)
  • O(c1cc4c(cc1)[C@H]3CC[C@]2([C@@H](CC[C@]2(C#C)O)[C@@H]3CC4)C)C
  • InChI=1S/C21H26O2/c1-4-21(22)12-10-19-18-7-5-14-13-15(23-3)6-8-16(14)17(18)9-11-20(19,21)2/h1,6,8,13,17-19,22H,5,7,9-12H2,2-3H3/t17-,18-,19+,20+,21+/m1/s1 checkY

Mestranol, sold under the brand names Enovid, Norinyl, and Ortho-Novum among others, is an estrogen medication which has been used in birth control pills, menopausal hormone therapy, and the treatment of menstrual disorders.[1][7][8][9] It is formulated in combination with a progestin and is not available alone.[9] It is taken by mouth.[1]

Side effects of mestranol include nausea, breast tension, edema, and breakthrough bleeding among others.[10] It is an estrogen, or an agonist of the estrogen receptors, the biological target of estrogens like estradiol.[11] Mestranol is a prodrug of ethinylestradiol in the body.[11]

Mestranol was discovered in 1956 and was introduced for medical use in 1957.[12][13] It was the estrogen component in the first birth control pill.[12][13] In 1969, mestranol was replaced by ethinylestradiol in most birth control pills, although mestranol continues to be used in a few birth control pills even today.[14][9] Mestranol remains available only in a few countries, including the United States, United Kingdom, Japan, and Chile.[9]

Medical uses[edit]

Mestranol was employed as the estrogen component in many of the first oral contraceptives, such as mestranol/noretynodrel (brand name Enovid) and mestranol/norethisterone (brand names Ortho-Novum, Norinyl), and is still in use today.[7][8][9] In addition to its use as an oral contraceptive, mestranol has been used as a component of menopausal hormone therapy for the treatment of menopausal symptoms.[1]

Side effects[edit]


Ethinylestradiol (EE), the active form of mestranol.

Mestranol is a biologically inactive prodrug of ethinylestradiol to which it is demethylated in the liver (via O-Dealkylation) with a conversion efficiency of 70% (50 μg of mestranol is pharmacokinetically bioequivalent to 35 μg of ethinylestradiol).[15][16][11] It has been found to possess 0.1 to 2.3% of the relative binding affinity of estradiol (100%) for the estrogen receptor, compared to 75 to 190% for ethinylestradiol.[17][18]

The elimination half-life of mestranol has been reported to be 50 minutes.[2] The elimination half-life of the active form of mestranol, ethinylestradiol, is 7 to 36 hours.[3][4][5][6]

The effective ovulation-inhibiting dosage of mestranol has been studied in women.[19][20][21] It has been reported to be about 98% effective at inhibiting ovulation at a dosage of 75 or 80 μg/day.[22][21][23] In another study, the ovulation rate was 15.4% at 50 μg/day, 5.7% at 80 μg/day, and 1.1% at 100 μg/day.[24]

Affinities and estrogenic potencies of estrogen esters and ethers at the estrogen receptors
Estrogen Other names RBA (%)a REP (%)b
Estradiol E2 100 100 100
Estradiol 3-sulfate E2S; E2-3S ? 0.02 0.04
Estradiol 3-glucuronide E2-3G ? 0.02 0.09
Estradiol 17β-glucuronide E2-17G ? 0.002 0.0002
Estradiol benzoate EB; Estradiol 3-benzoate 10 1.1 0.52
Estradiol 17β-acetate E2-17A 31–45 24 ?
Estradiol diacetate EDA; Estradiol 3,17β-diacetate ? 0.79 ?
Estradiol propionate EP; Estradiol 17β-propionate 19–26 2.6 ?
Estradiol valerate EV; Estradiol 17β-valerate 2–11 0.04–21 ?
Estradiol cypionate EC; Estradiol 17β-cypionate ?c 4.0 ?
Estradiol palmitate Estradiol 17β-palmitate 0 ? ?
Estradiol stearate Estradiol 17β-stearate 0 ? ?
Estrone E1; 17-Ketoestradiol 11 5.3–38 14
Estrone sulfate E1S; Estrone 3-sulfate 2 0.004 0.002
Estrone glucuronide E1G; Estrone 3-glucuronide ? <0.001 0.0006
Ethinylestradiol EE; 17α-Ethynylestradiol 100 17–150 129
Mestranol EE 3-methyl ether 1 1.3–8.2 0.16
Quinestrol EE 3-cyclopentyl ether ? 0.37 ?
Footnotes: a = Relative binding affinities (RBAs) were determined via in-vitro displacement of labeled estradiol from estrogen receptors (ERs) generally of rodent uterine cytosol. Estrogen esters are variably hydrolyzed into estrogens in these systems (shorter ester chain length -> greater rate of hydrolysis) and the ER RBAs of the esters decrease strongly when hydrolysis is prevented. b = Relative estrogenic potencies (REPs) were calculated from half-maximal effective concentrations (EC50) that were determined via in-vitro β‐galactosidase (β-gal) and green fluorescent protein (GFP) production assays in yeast expressing human ERα and human ERβ. Both mammalian cells and yeast have the capacity to hydrolyze estrogen esters. c = The affinities of estradiol cypionate for the ERs are similar to those of estradiol valerate and estradiol benzoate (figure). Sources: See template page.
Potencies of oral estrogens[data sources 1]
Compound Dosage for specific uses (mg usually)[a]
ETD[b] EPD[b] MSD[b] MSD[c] OID[c] TSD[c]
Estradiol (non-micron.) 30 ≥120–300 120 6 - -
Estradiol (micronized) 6–12 60–80 14–42 1–2 >5 >8
Estradiol valerate 6–12 60–80 14–42 1–2 - >8
Estradiol benzoate - 60–140 - - - -
Estriol ≥20 120–150[d] 28–126 1–6 >5 -
Estriol succinate - 140–150[d] 28–126 2–6 - -
Estrone sulfate 12 60 42 2 - -
Conjugated estrogens 5–12 60–80 8.4–25 0.625–1.25 >3.75 7.5
Ethinylestradiol 200 μg 1–2 280 μg 20–40 μg 100 μg 100 μg
Mestranol 300 μg 1.5–3.0 300–600 μg 25–30 μg >80 μg -
Quinestrol 300 μg 2–4 500 μg 25–50 μg - -
Methylestradiol - 2 - - - -
Diethylstilbestrol 2.5 20–30 11 0.5–2.0 >5 3
DES dipropionate - 15–30 - - - -
Dienestrol 5 30–40 42 0.5–4.0 - -
Dienestrol diacetate 3–5 30–60 - - - -
Hexestrol - 70–110 - - - -
Chlorotrianisene - >100 - - >48 -
Methallenestril - 400 - - - -
Sources and footnotes:
  1. ^ Dosages are given in milligrams unless otherwise noted.
  2. ^ a b c Dosed every 2 to 3 weeks
  3. ^ a b c Dosed daily
  4. ^ a b In divided doses, 3x/day; irregular and atypical proliferation.


Mestranol, also known as ethinylestradiol 3-methyl ether (EEME) or as 17α-ethynyl-3-methoxyestra-1,3,5(10)-trien-17β-ol, is a synthetic estrane steroid and a derivative of estradiol.[43][44][45] It is specifically a derivative of ethinylestradiol (17α-ethynylestradiol) with a methyl ether at the C3 position.[43][44]


In April 1956, noretynodrel was investigated, in Puerto Rico, in the first large-scale clinical trial of a progestogen as an oral contraceptive.[12][13] The trial was conducted in Puerto Rico due to the high birth rate in the country and concerns of moral censure in the United States.[46] It was discovered early into the study that the initial chemical syntheses of noretynodrel had been contaminated with small amounts (1–2%) of the 3-methyl ether of ethinylestradiol (noretynodrel having been synthesized from ethinylestradiol).[12][13] When this impurity was removed, higher rates of breakthrough bleeding occurred.[12][13] As a result, mestranol, that same year (1956),[47] was developed and serendipitously identified as a very potent synthetic estrogen (and eventually as a prodrug of ethinylestradiol), given its name, and added back to the formulation.[12][13] This resulted in Enovid by G. D. Searle & Company, the first oral contraceptive and a combination of 9.85 mg noretynodrel and 150 μg mestranol per pill.[12][13]

Around 1969, mestranol was replaced by ethinylestradiol in most combined oral contraceptives due to widespread panic about the recently uncovered increased risk of venous thromboembolism with estrogen-containing oral contraceptives.[14] The rationale was that ethinylestradiol was approximately twice as potent by weight as mestranol and hence that the dose could be halved, which it was thought might result in a lower incidence of venous thromboembolism.[14] Whether this actually did result in a lower incidence of venous thromboembolism has never been assessed.[14]

Society and culture[edit]

Generic names[edit]

Mestranol is the generic name of the drug and its INN, USAN, USP, BAN, DCF, and JAN, while mestranolo is its DCIT.[43][44][1][9]

Brand names[edit]

Mestranol has been marketed under a variety of brand names, mostly or exclusively in combination with progestins, including Devocin, Enavid, Enovid, Femigen, Mestranol, Norbiogest, Ortho-Novin, Ortho-Novum, Ovastol, and Tranel among others.[7][43][48][44] Today, it continues to be sold in combination with progestins under brand names including Lutedion, Necon, Norinyl, Ortho-Novum, and Sophia.[9]


Mestranol remains available only in the United States, the United Kingdom, Japan, and Chile.[9] It is only marketed in combination with progestins, such as norethisterone.[9]


Mestranol has been studied as a male contraceptive and was found to be highly effective.[49][50][51][52] At a dosage of 0.45 mg/day, it suppressed gonadotropin levels, reduced sperm count to zero within 4 to 6 weeks, and decreased libido, erectile function, and testicular size.[49][50][52][51] Gynecomastia occurred in all of the men.[49][50][52][51] These findings contributed to the conclusion that estrogens would be unacceptable as contraceptives for men.[50]


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