Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ELAGOLIX vs ESTROSTEP 21
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Gonadotropin-releasing hormone (Gn RH) receptor antagonist that competitively binds to Gn RH receptors in the anterior pituitary, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release, thereby suppressing ovarian estradiol production.
Estrostep 21 is a combination oral contraceptive containing ethinyl estradiol and norethindrone acetate. It works primarily by suppressing gonadotropin-releasing hormone (Gn RH) from the hypothalamus, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion from the pituitary, thereby inhibiting ovulation. Additionally, it thickens cervical mucus to impede sperm penetration and alters the endometrium to reduce implantation likelihood.
Management of moderate to severe pain associated with endometriosis
Prevention of pregnancy,Treatment of moderate acne vulgaris in females >= 15 years of age who have achieved menarche, are not pregnant, and desire oral contraception
200 mg orally twice daily
One tablet orally once daily for 21 days, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg.
Terminal elimination half-life is approximately 4–6 hours. Clinical context: Steady state achieved within 5 days; tid dosing maintains therapeutic concentrations.
Ethinyl estradiol: 13-27 hours (terminal); norethindrone acetate: 5-14 hours (terminal). Steady-state achieved within 3-5 days.
Primarily metabolized by CYP3A4; minor contribution from CYP2D6 and CYP2C8.
Ethinyl estradiol is metabolized primarily via CYP3A4 and undergoes glucuronidation and sulfation. Norethindrone acetate is deacetylated to norethindrone, which is metabolized by CYP3A4 and other CYP enzymes, and undergoes reduction and glucuronidation.
Renal (approximately 70% as unchanged drug and metabolites), fecal (approximately 30%)
Biliary/fecal (40-50% as metabolites) and renal (30-40% as glucuronide and sulfate conjugates)
Approximately 99% bound to albumin and alpha-1-acid glycoprotein
Ethinyl estradiol: 97-98% bound to albumin; norethindrone: 95-97% bound to albumin and SHBG.
Vd/F is approximately 40–60 L (0.5–0.8 L/kg). Clinical meaning: Extensive tissue distribution, consistent with a large volume of distribution.
Ethinyl estradiol: 2.5-4.5 L/kg; norethindrone: 3.5-5.5 L/kg. Indicates extensive tissue distribution.
Oral: Approximately 30% (low due to first-pass metabolism); food increases exposure by approximately 30%.
Ethinyl estradiol: 38-48% (oral, first-pass metabolism); norethindrone acetate: 50-70% (oral, deacetylation to norethindrone).
e GFR 30-89 m L/min: no adjustment. e GFR 15-29 m L/min: 100 mg twice daily. e GFR <15 m L/min: not recommended.
No dose adjustment required for mild to moderate renal impairment. Contraindicated in severe renal impairment or acute renal failure.
Child-Pugh A: no adjustment. Child-Pugh B: 100 mg twice daily. Child-Pugh C: not recommended.
Contraindicated in acute hepatitis, severe cirrhosis, benign or malignant liver tumors, or Child-Pugh class C cirrhosis. Use with caution in Child-Pugh class A or B; consider alternative therapy.
Not established; safety and efficacy in pediatric patients have not been studied.
Not indicated for use before menarche. Post-menarche: same dosing as adults; use lowest effective dose for shortest duration.
No specific dose adjustment required; clinical studies included limited patients ≥65 years, but no differences in safety or efficacy observed.
Not indicated for postmenopausal women; no established dosing in elderly. Consider alternative therapies as necessary.
None
Cigarette smoking increases the risk of serious cardiovascular events from oral contraceptive use. This risk increases with age (especially in women > 35 years) and with the number of cigarettes smoked. Women who use oral contraceptives should be strongly advised not to smoke.
Hepatic transaminase elevations: monitor liver function before and during treatment; discontinue if elevation >3x ULN or if signs of liver injury occur.,Bone density loss: monitor bone mineral density with long-term use; consider additional calcium/vitamin D.,Mood changes: increased risk of depression, suicidal ideation; monitor for new or worsening symptoms.,Altered menstrual bleeding; exclude pregnancy before starting.,Risk of osteoporosis with prolonged use.
Increased risk of thromboembolic disorders (e.g., venous thromboembolism, stroke, myocardial infarction), especially in smokers and women over 35,Hepatic neoplasia (benign and malignant) reported,Hypertension and gallbladder disease,Carbohydrate and lipid effects; monitor in diabetic patients,Ocular lesions (e.g., retinal thrombosis); discontinue if unexplained vision loss or proptosis occurs,Hereditary angioedema exacerbation,Chloasma; avoid sun exposure,Menstrual irregularities (e.g., breakthrough bleeding, amenorrhea),Depression; discontinue if severe
Known hypersensitivity to elagolix or any excipients,Concomitant use with strong organic anion-transporting polypeptide (OATP) 1B1 inhibitors (e.g., cyclosporine, gemfibrozil),Pregnancy, or women of reproductive potential not using effective contraception,Existing osteoporosis or severe bone loss,History of suicidal ideation or behavior
Thrombophlebitis, thromboembolic disorders, or history thereof (e.g., deep vein thrombosis, pulmonary embolism),Cerebrovascular disease (e.g., stroke, TIA),Coronary artery disease (e.g., myocardial infarction, angina),Known or suspected breast cancer, endometrial cancer, or other estrogen-dependent neoplasia,Undiagnosed abnormal genital bleeding,Cholestatic jaundice of pregnancy or jaundice with prior oral contraceptive use,Benign or malignant liver tumors,Known or suspected pregnancy,Hypersensitivity to any component,Smoking in women over 35 years of age
Avoid grapefruit and grapefruit juice as they inhibit CYP3A4 and may increase elagolix levels. No other food restrictions.
No specific food interactions. Grapefruit juice may increase estrogen exposure (mild effect). Maintain consistent timing with meals to reduce nausea if needed. Avoid alcohol if liver function is compromised.
First trimester: High risk of pregnancy loss and major birth defects based on animal data and mechanism of action. Second and third trimesters: Contraindicated due to potential for harm. Elagolix is contraindicated in pregnancy.
Estrostep 21 (norethindrone acetate/ethinyl estradiol) is contraindicated in pregnancy. First trimester: increased risk of cardiovascular malformations, limb reduction defects, and neural tube defects. Second and third trimesters: associated with fetal genital abnormalities, feminization of male fetuses, and potential long-term reproductive effects. Use in early pregnancy for emergency contraception is not recommended due to potential risks.
Elagolix is excreted in animal milk; no human data. M/P ratio unknown. Not recommended during breastfeeding.
Estrostep 21 is excreted in breast milk in small amounts; ethinyl estradiol M/P ratio approximately 0.1; norethindrone M/P ratio ~0.5. May reduce milk production and quality, especially in early lactation. Use generally avoided during breastfeeding; consider progestin-only alternatives.
No dose adjustments studied; contraindicated in pregnancy. No data on PK changes requiring dose modification.
Estrostep 21 is contraindicated in pregnancy; no dose adjustments recommended as use is avoided. Pharmacokinetic changes during pregnancy (increased hepatic metabolism, volume of distribution) would require dose adjustment if used, but due to risks, alternative therapy is indicated.
Elagolix is an oral Gn RH antagonist for endometriosis-associated pain. Monitor bone mineral density (BMD) with dual-energy X-ray absorptiometry (DXA) if using >12 months or in patients with osteoporosis risk. Avoid use with strong CYP3A inducers (e.g., rifampin) or inhibitors (e.g., ketoconazole). May reduce efficacy of hormonal contraceptives. Assess pregnancy status before starting due to teratogenicity.
ESTROSTEP 21 is a monophasic oral contraceptive containing norethindrone acetate and ethinyl estradiol. Due to its low estrogen dose (20 mcg), it may be associated with more breakthrough bleeding compared to higher-dose pills. It is indicated for contraception and may be used for acne treatment. The 21-day regimen requires a 7-day hormone-free interval. Counsel patients that smoking increases the risk of serious cardiovascular adverse effects; avoid in women over 35 who smoke.
Take elagolix at the same time daily with or without food.,Avoid grapefruit or grapefruit juice during treatment.,Use non-hormonal contraception (e.g., condoms) because elagolix may reduce hormonal contraceptive effectiveness.,Report severe headaches, vision changes, or heavy bleeding promptly.,Do not take elagolix if pregnant or planning to become pregnant; use effective birth control.
Take one tablet daily at the same time each day for 21 days, then no pills for 7 days.,If you miss a dose, follow the package instructions; use backup contraception if missed more than one tablet.,Do not smoke while taking this medication; smoking increases risk of blood clots, stroke, and heart attack, especially if over 35.,Common side effects include spotting, nausea, breast tenderness, and headache; these often improve after a few cycles.,Seek emergency care if you have signs of a blood clot: sudden leg pain, chest pain, shortness of breath, or vision changes.,This medication does not protect against HIV or other sexually transmitted infections.,Take missed pills as soon as remembered; do not take more than two tablets in one day.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ELAGOLIX vs ESTROSTEP 21, answered by our medical review team.
ELAGOLIX is a Gonadotropin-Releasing Hormone Antagonist that works by Gonadotropin-releasing hormone (Gn RH) receptor antagonist that competitively binds to Gn RH receptors in the anterior pituitary, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release, thereby suppressing ovarian estradiol production.. ESTROSTEP 21 is a Combined Oral Contraceptive that works by Estrostep 21 is a combination oral contraceptive containing ethinyl estradiol and norethindrone acetate. It works primarily by suppressing gonadotropin-releasing hormone (Gn RH) from the hypothalamus, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion from the pituitary, thereby inhibiting ovulation. Additionally, it thickens cervical mucus to impede sperm penetration and alters the endometrium to reduce implantation likelihood.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ELAGOLIX and ESTROSTEP 21 depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ELAGOLIX is: 200 mg orally twice daily. The standard adult dose of ESTROSTEP 21 is: One tablet orally once daily for 21 days, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ELAGOLIX and ESTROSTEP 21 in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ELAGOLIX is classified as Category C. First trimester: High risk of pregnancy loss and major birth defects based on animal data and mechanism of action. Second and third trimesters: Contraindicated due to potential for. ESTROSTEP 21 is classified as Category C. Estrostep 21 (norethindrone acetate/ethinyl estradiol) is contraindicated in pregnancy. First trimester: increased risk of cardiovascular malformations, limb reduction defects, and. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.