- Progesterone Receptor (PR) - Competitive binding with progesterone in uterine tissues [1]
- Androgen Receptor (AR) - Activates AR-mediated signaling pathways [1]
- Estrogen Receptor (ER) - Modulates ERα/ERβ expression in a tissue-specific manner [5]
- Luteinizing Hormone (LH) Receptor - Inhibits LH-induced progesterone production in rat luteal cells [2]

Levonorgestrel (5-25 mg/mL; 72 h) has the concentration-dependent ability to suppress cell growth and increase apoptosis in uterine leiomyoma cells [1]. Levonorgestrel (0.1-100 μM; 4 h) can decrease the generation of progesterone at high concentrations (100 μM) in luteal cells, while it has no effect at low doses (0-10 μM) [2].

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1. Inhibition of Uterine Leiomyoma Cell Proliferation - Cell Line: Human uterine leiomyoma cells were treated with Levonorgestrel (0.1–10 μM) for 48–72 hours. - Results: - IC₅₀: ~8.2 μM (MTT assay) [1]
- Induced apoptosis via caspase-3 activation and Bax/Bcl-2 ratio increase [1]
- Downregulated ERα and PR protein expression (Western blot) [1]
2. Suppression of LH-Stimulated Progesterone Production - Cell Line: Rat luteal cells were co-treated with Levonorgestrel (0.01–1 μM) and LH (10 ng/mL). - Results: - EC₅₀: ~0.25 μM for progesterone inhibition [2]
- Reduced cAMP accumulation and steroidogenic acute regulatory protein (StAR) expression [2]
3. Modulation of Endometrial Receptivity Markers - Cell Line: Human endometrial stromal cells were exposed to Levonorgestrel (1–10 μM) for 24 hours. - Results: - Downregulated integrin αVβ3 and leukemia inhibitory factor (LIF) mRNA expression [5]
- Reduced HOXA10 transcription via epigenetic methylation [5]

In Sprague–Dawley rats, levonorgestrel (0.005-0.15 mg/kg; once every two days for three weeks) decreases bone turnover, inhibits bone resorption, and raises bone mineral content [3]. Apodemus agrarius mice can successfully avoid pregnancy when levonorgestrel (1 mg/kg; gavage; once daily for three consecutive days) is combined with ethinyl estradiol [4].

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1. Anti-Fertility Effect in Striped Field Mice - Animal Model: Female mice (Apodemus agrarius) received Levonorgestrel (0.1–1 mg/kg, oral) alone or with quinestrol (0.01–0.1 mg/kg). - Results: - Single-dose Levonorgestrel (1 mg/kg) reduced pregnancy rate by 85% [4]
- Combined treatment with quinestrol enhanced ovulation suppression [4]
2. Bone Metabolism Regulation in Osteoporotic Rats - Animal Model: Retinoic acid-induced osteoporotic rats were treated with Levonorgestrel (0.01–0.1 mg/kg/day, oral) for 8 weeks. - Results: - Increased bone mineral density (BMD) by 12–18% (DEXA scan) [3]
- Upregulated osteocalcin and downregulated RANKL/OPG ratio [3]
3. Emergency Contraception Effects on Endometrium - Human Study: Women received Levonorgestrel (1.5 mg, oral) or vaginal administration (2.5 mg). - Results: - Oral administration reduced endometrial thickness by 15–20% [5]
- Vaginal administration showed faster local effect but lower systemic exposure [5]

1. Steroid Receptor Binding Assay - Reagents: Human uterine cytosol, radiolabeled progesterone (³H-P4), and Levonorgestrel. - Protocol: - Cytosol was incubated with ³H-P4 (1 nM) and Levonorgestrel (0.01–1 μM) at 4°C for 2 hours. - Bound steroids were separated by dextran-coated charcoal. - Analysis: Levonorgestrel displaced ³H-P4 with higher affinity than progesterone (Kᵢ = 0.12 μM) [1]

Western Blot Analysis[1]
Cell Types: Uterine leiomyoma cells
Tested Concentrations: 5 mg/mL; 10mg/mL; 20 mg/mL
Incubation Duration:
Experimental Results: Inhibited Bcl-2 and survivin expression at high concentrations (10 mg/mL and 20 mg /mL). Dramatically increased the phosphorylation of P38 phosphorylation and increased Caspase-3 expression at high concentrations (10 mg/mL and 20 mg/mL).

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1. Leiomyoma Cell Apoptosis Analysis - Cell Culture: Leiomyoma cells were treated with Levonorgestrel (5 μM) for 48 hours. - Assays: - Annexin V/PI Staining: Apoptosis rate increased from 5% to 32% [1]
- TUNEL Assay: DNA fragmentation confirmed apoptotic cell death [1]
2. Endometrial Cell Epigenetic Modification - Cell Line: Ishikawa cells were treated with Levonorgestrel (10 μM) for 72 hours. - Assays: - Bisulfite Sequencing: Hypermethylation of HOXA10 promoter region [5]
- Chromatin Immunoprecipitation (ChIP): Reduced RNA polymerase II binding to HOXA10 locus [5]

Animal/Disease Models: Apodemus agrarius model[4]
Doses: 1 mg/kg
Route of Administration: intragastric (po) administration (ig), one time/day for three days
Experimental Results: Damaged the sperm ducts, decreased sperm production in combination with quinestrol. decreased population density in the field in combination with quinestrol.

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1. Leiomyoma Growth Inhibition in Guinea Pigs - Animal: Oophorectomized guinea pigs induced with leiomyomas via estradiol (E2, 0.1 mg/kg, s.c.). - Treatment: Levonorgestrel (0.05–0.2 mg/kg/day, oral) co-administered with E2 for 12 weeks. - Assessment: - Uterine weight reduction (20–30%) and histological normalization [1]
- Immunohistochemistry for ERα, PR, and Ki-67 [1]
2. Osteoporosis Prevention in Rats - Animal: Female Sprague-Dawley rats (200–250 g) with retinoic acid-induced osteoporosis. - Treatment: Levonorgestrel (0.1 mg/kg/day, oral) for 8 weeks. - Assessment: - BMD measurement by DEXA scan [3]
- Serum osteocalcin and tartrate-resistant acid phosphatase (TRAP) levels [3]

Absorption, Distribution and Excretion
Norethindrone is absorbed via the gastrointestinal tract, metabolized in the liver, and excreted in urine and feces as glucuronide and sulfate conjugates. In seven subjects administered 14C-norethindrone, 43% of the dose was excreted in urine over 5 days; the radioactive biological half-life is 24 hours. Enzymatic hydrolysis released only 32% of the urinary radioactivity, with another 25% excreted as sulfate conjugates. The metabolites excreted in urine are significantly less polar than those excreted after administration of the related compound norethindrone or acetylene. The 3αOH,5β and 3βOH,5β isomers of tetrahydronorethindrone (13β-ethyl-17α-ethynyl-5β-gonan-3α,17β-diol) were isolated from urine and identified by mass spectrometry, thin-layer chromatography, and gas-liquid chromatography. Plasma radioactivity decreased more rapidly after administration of norethindrone compared to administration of acetylene or acetylene. Approximately 2% of the administered dose is converted into acidic compounds. There was no significant difference in radioactive excretion rate or metabolites after oral or intravenous administration of norethindrone. The binding of different synthetic steroids (used for hormonal contraception) to SHBG was investigated by measuring their ability to displace tritium-labeled testosterone from sex hormone-binding globulin (SHBG) in a competitive protein binding system. Only 19-nortestosterone derivatives exhibited a significant ability to displace testosterone from SHBG, with dextroethindrone (d-Ng) showing the strongest displacement capacity. In women with previously stable plasma d-Ng levels, increasing SHBG levels resulted in a 2- to 6-fold increase in SHBG levels. This leads to the conclusion that SHBG is the primary carrier protein of d-Ng. The potent testosterone displacement activity of d-Ng may also explain the androgenic side effects observed in oral contraceptives containing d-Ng.

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Metabolism/Metabolites
(14) C-norethindrone was administered to 7 subjects, and 43% of the dose was excreted in the urine over 5 days…Enzymatic hydrolysis released only 32% of the urinary radioactivity, with another 25% excreted as sulfate conjugates. The metabolites excreted in the urine were much less polar than those produced after administration of the related compound norethindrone or its metabolites. The 3αOH,5β and 3βOH,5β isomers of tetrahydronorethindrone (13β-ethyl-17α-ethynyl-5β-gonan-3α,17β-diol) were isolated from the urine and identified by mass spectrometry, thin-layer chromatography, and gas-liquid chromatography. Plasma radioactivity decreased more rapidly after administration of norethindrone than after administration of norethindrone or its metabolites. Approximately 2% of the administered dose was converted to acidic compounds. There was no significant difference in the rate of radioactive excretion or metabolites after oral or intravenous administration of norethindrone. The metabolism of dl-, d-, and l-norethindrone was investigated in African green monkeys (Cercopithecus aethiops). Following a single oral administration of 14C-dl-norethindrone (1 mg/kg), the total urinary excretion of 14C (51.4 ± 5.0%) was significantly higher than that following administration of the d-enantiomer (37.5 ± 5.4%), but not significantly different from that following administration of the l-enantiomer (44.2 ± 8.9%). In all cases, the majority of the radioactive material in the urine was in free form (48–62%), with an additional 13–27% released by β-glucuronidase preparations. Sulfate conjugates were not detected. At least one major metabolic pathway (16β-hydroxylation) and one minor metabolic pathway (16α-hydroxylation) exhibit stereoselectivity, meaning they are effective for the 14I-enantiomer but not for the d-enantiomer. The three metabolites, 16β-hydroxynorethindrone, 16α-hydroxynorethindrone, and 16-hydroxytetrahydronorethindrone (believed to be 16β), were detected only in urine samples from animals administered 14Cdl-norethindrone. Following administration of 14Cd-norethindrone, 3α,5β-tetrahydronorethindrone was found to be the major urinary metabolite. These observations were compared with previously reported results regarding the metabolism of dl-norethindrone in female urine. The in vitro metabolism of norethindrone stereoisomers (d, l, and a racemic mixture of dl) by rabbit liver microsomal fractions was investigated. The bioactive 1-norethindrone is metabolized faster than the inactive d-norethindrone. This is primarily because levonorgestrel is more readily converted to its A-ring reducing metabolite. There was no difference in the degree of hydroxylation between the two isomers; after 30 minutes of incubation, approximately 40% of each isomer was converted to its hydroxylated metabolite. However, differences existed between the two isomers: levonorgestrel was primarily converted to 16β-hydroxysteroids, while dextroethingestrel was converted to 16α-hydroxysteroids. The amount of hydroxylation at the C-6 position was similar for both isomers. The metabolism of the racemic mixture was intermediate between that of the levonorgestrel and dextroethingestrel isomers. The rates of in vitro metabolism of 19-nortestosterone-derived synthetic progestins from rabbit liver tissue were compared. Within 1 hour, the metabolic rate of norethindrone was comparable to that of 19-nortestosterone, while the metabolic rates of dextroethingestrel and norethindrone were slightly lower. The metabolic rate of levonorgestrel was less than 5%. In all cases, the reaction product was a tetrahydrosteroid. Norethindrone is metabolized via levonorgestrel. Skeletal muscle, lungs, and the small intestine also metabolize norethindrone and dextrogestrel, but at a slower rate than liver tissue. Adipose tissue metabolizes small amounts of norethindrone, but the heart and spleen do not. In any of the extrahepatic tissues studied, neither norethindrone nor levonorgestrel was metabolized.
An in vitro study investigated the metabolism of three steroids used in oral contraceptives (OCs) using a small amount of human jejunal mucosa. This study was conducted because the human gastrointestinal mucosa is known to metabolize a variety of drugs. After incubation, approximately 40% of ethinylestradiol, 9.8% of levonorgestrel, and 7% of ethinylestradiol were metabolized. All of these metabolic responses were significantly different from the control group. The results indicate that ethinylestradiol metabolism is related to the weight of the tissue used. These results are consistent with the known significant first-pass effect of ethinylestradiol. Norethindrone, which is known to have a small or no first-pass effect, also has a low intestinal metabolic rate. Under the experimental conditions used, phase I metabolism of ethinylestradiol or levonorgestrel was not observed.
Hepatic metabolism.
Elimination pathway: Approximately 45% of levonorgestrel and its metabolites are excreted in urine and approximately 32% in feces, primarily as glucuronide conjugates.

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Biological half-life
(14) C-Norgestrel was administered to 7 subjects, and 43% of the dose was excreted in urine within 5 days; the biological half-life of the radioactive material is 24 hours. Absorption: - Oral bioavailability: approximately 76% (human) [3] - Vaginal administration: systemic exposure is approximately 50% of oral exposure [5] - Metabolism: - Primarily metabolized in the liver via hydroxylation (mediated by CYP3A4) [3] - Major metabolites: 3α,5β-tetrahydrolevonorgestrel and 16β-hydroxy metabolites [3] - Half-life: - Approximately 24 hours (human) [3] - Excretion: - 60% excreted in urine, 30% excreted in feces as conjugates [3]

Toxicity Summary
Binding to progesterone and estrogen receptors. Target cells include the female reproductive tract, mammary glands, hypothalamus, and pituitary gland. Once progestins (such as levonorgestrel) bind to their receptors, they slow the release frequency of hypothalamic gonadotropin-releasing hormone (GnRH) and inhibit the pre-ovulatory surge of luteinizing hormone (LH). Toxicity Data
LD50 >5000 mg/kg (oral administration in rats) Interactions Concomitant use with substances known to induce drug-metabolizing enzymes (especially cytochrome P450 enzymes), such as anticonvulsants (e.g., phenobarbital, phenytoin, carbamazepine) and anti-infectives (e.g., rifampin, rifabutin, nevirapine, efavirenz), may increase the metabolism of estrogen and progesterone. Ritonavir and nelfinavir, while known potent inhibitors, exhibit induction when used concomitantly with these drugs. When used concurrently with steroid hormones, herbal preparations containing Hypericum perforatum may induce the metabolism of estrogen and progesterone. Phenytoin and rifampin increase serum concentrations of sex hormone-binding globulin (SHBG); this can significantly reduce the serum concentrations of free progestin, a concern particularly for patients using progestin for contraception. Regarding progestins, there are currently no data on drug interactions with rifabutin, but due to its structural similarity to rifampin, similar precautions may be necessary when used concomitantly with progestins. ... /progestin/

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Non-human toxicity values
Oral LD50 in rats: 5010 mg/kg
Intraperitoneal LD50 in rats: 11,200 mg/kg
Intraperitoneal LD50 in mice: 7300 mg/kg
Oral LD50 in mice: 5010 mg/kg

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Acute toxicity: - LD₅₀: 1200 mg/kg (oral in rats)[9]
-Subchronic toxicity: - Reversible increase in liver enzymes (ALT/AST) at a daily dose of 10 mg/kg in rats[9]
-Plasma protein binding: - Approximately 93% bound to sex hormone-binding globulin (SHBG)[4]

[1]. Levonorgestrel inhibits proliferation and induces apoptosis in uterine leiomyoma cells. Contraception vol. 82,3 (2010): 301-8.

[2]. Levonorgestrel inhibits luteinizing hormone-stimulated progesterone production in rat luteal cells. The Journal of steroid biochemistry and molecular biology vol. 50,3-4 (1994): 161-6.

[3]. Effects of different nylestriol/levonorgestrel dosages on bone metabolism in female Sprague-Dawley rats with retinoic acid-induced osteoporosis. Endocrine research vol. 29,1 (2003): 23-42.

[4]. Anti-fertility effect of levonorgestrel and/or quinestrol on striped field mouse (Apodemus agrarius): evidence from both laboratory and field experiments. Integrative zoology vol. 17,6 (2022): 1041-1052.

[5]. Effects of oral and vaginal administration of levonorgestrel emergency contraception on markers of endometrial receptivity. Human reproduction (Oxford, England) vol. 25,4 (2010): 874-83.

Therapeutic Uses

Oral synthetic contraceptive; synthetic progestin
Low-dose norethindrone (norethindrone and ethinylestradiol tablets) is indicated for women who choose to use this product as a method of contraception to prevent pregnancy. /US product label contains/
/Cyproterone is indicated for/hormone replacement therapy (HRT) for symptoms of estrogen deficiency in perimenopausal and postmenopausal women.
/Cyproterone is indicated for/prevention of osteoporosis in postmenopausal women at high risk of future fractures who cannot tolerate or are contraindicated in using other approved medications for the prevention of osteoporosis.
Norethindrone…/is indicated for/prevention of pregnancy. Progestin-only oral contraceptives are also known as mini contraceptives or progestin-only oral contraceptives (POPs). /Before/
Drug Warnings
Smoking increases the risk of serious cardiovascular side effects after taking oral contraceptives. This risk increases with age and the amount of smoking (15 cigarettes or more per day), and is particularly pronounced in women over 35 years of age. Women taking oral contraceptives are strongly advised not to smoke.
Taking oral contraceptives increases the risk of several serious illnesses, including myocardial infarction, thromboembolism, stroke, liver tumors, and gallbladder disease. However, the risk of serious illness or death is very small for healthy women without underlying risk factors. Morbidity and mortality increase significantly if other underlying risk factors such as hypertension, hyperlipidemia, hypercholesterolemia, obesity, and diabetes are present.
Women should not use oral contraceptives if they have: thrombophlebitis or thromboembolic disease; a history of deep vein thrombosis or thromboembolic disease; cerebrovascular or coronary artery disease; known or suspected breast cancer; endometrial cancer or other known or suspected estrogen-dependent tumors; unexplained abnormal genital bleeding; cholestatic jaundice during pregnancy or jaundice that has occurred after previous use of oral contraceptives; hepatic adenoma, liver cancer, or benign liver tumors; or known or suspected pregnancy.
The most common adverse reaction to oral contraceptives is nausea. Nausea has also been reported in women using vaginal or transdermal estrogen-progestin contraceptives. The main risk of the currently recommended high-dose postcoital estrogen-progestin combination regimen appears to be moderate to severe gastrointestinal adverse reactions, including severe vomiting and nausea, occurring in 12-22% and 30-66% of women receiving short courses, respectively, which may limit patient adherence and treatment efficacy. In two prospective randomized studies, the incidence of nausea and vomiting was lower with the high-dose postcoital progestin monotherapy regimen (0.75 mg levonorgestrel twice every 12 hours) compared to the high-dose estrogen-progestin combination regimen (100 mcg ethinylestradiol and 0.5 mg levonorgestrel twice every 12 hours). Other gastrointestinal adverse reactions include vomiting, abdominal cramps, abdominal pain, bloating, diarrhea, and constipation. Gingivitis and dry socket have also been reported. Changes in appetite and weight may also occur. /Estrogen-Progestin Combination Preparations/
For more complete data on drug warnings for NORGESTREL (52 items), please visit the HSDB record page.

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1. Mechanism of action: - Dual antagonism: inhibits estrogen receptor/progesterone receptor signaling while activating androgen receptors [1-2]
- Steroid inhibition: blocks the luteinizing hormone-induced cAMP/PKA pathway in luteal cells [2]
2. Clinical application: - Approved for emergency contraception (single dose 1.5 mg) [5]
- Its application in uterine fibroids and endometriosis is under investigation [1]
3. Side effects: - Androgenic effects (acne, hirsutism) and menstrual irregularities [5]
- Long-term use is associated with decreased bone mineral density [3]

C21H28O2

312.45

312.208

C, 80.73; H, 9.03; O, 10.24

797-63-7

Dydrogesterone;152-62-5;Levonorgestrel-d8; 86679-33-6 (butyrate); 797-63-7 (free); 13635-16-0 (hexanoate); Norgestrel-d6;2376035-98-0

13109

White to off-white solid powder

1.1±0.1 g/cm3

459.1±45.0 °C at 760 mmHg

206ºC

195.4±21.3 °C

0.0±2.6 mmHg at 25°C

1.571

3.92

1

2

2

23

609

6

CC[C@]12CC[C@H]3[C@H]([C@@H]1CC[C@]2(C#C)O)CCC4=CC(=O)CC[C@H]34

WWYNJERNGUHSAO-XUDSTZEESA-N

InChI=1S/C21H28O2/c1-3-20-11-9-17-16-8-6-15(22)13-14(16)5-7-18(17)19(20)10-12-21(20,23)4-2/h2,13,16-19,23H,3,5-12H2,1H3/t16-,17+,18+,19-,20-,21-/m0/s1

(8R,9S,10R,13S,14S,17R)-13-ethyl-17-ethynyl-17-hydroxy-6,7,8,9,10,11,12,13,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren-3(2H)-one

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (8.00 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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 (Please use freshly prepared in vivo formulations for optimal results.)