Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
KARIVA vs ESTROSTEP FE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Combination of ethinyl estradiol (estrogen) and levonorgestrel (progestin) that inhibits gonadotropin release, suppressing ovulation, altering cervical mucus to impede sperm penetration, and changing endometrial receptivity.
Combination estrogen-progestin contraceptive: ethinyl estradiol suppresses gonadotropin release via negative feedback on hypothalamic-pituitary axis; norethindrone acetate produces progestational effects including endometrial transformation and cervical mucus thickening, inhibiting sperm penetration and implantation.
Prevention of pregnancy,Management of heavy menstrual bleeding (off-label),Treatment of acne (off-label),Treatment of dysmenorrhea (off-label),Endometriosis pain relief (off-label)
Prevention of pregnancy,Treatment of moderate acne vulgaris (in females ≥15 years with no known contraindications, who have achieved menarche)
One tablet (0.15 mg levonorgestrel/0.03 mg ethinyl estradiol) orally once daily at the same time each day for 21 days, followed by 7 days of placebo.
One tablet daily orally, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg (24 active tablets) followed by ferrous fumarate 75 mg tablets (4 placebo tablets).
Terminal elimination half-life is 4.5 hours; in renal impairment (Cr Cl <30 m L/min), half-life may extend to 8-10 hours, requiring dose adjustment.
Ethinyl estradiol: 13-27 hours (terminal); norethindrone acetate: 5-14 hours. Clinical context: Steady-state reached within 7-10 days.
Hepatic via CYP3A4 for both ethinyl estradiol and levonorgestrel; undergoes conjugation (glucuronidation and sulfation). Ethinyl estradiol also undergoes oxidative metabolism. Levonorgestrel is reduced and conjugated.
Ethinyl estradiol: primarily metabolized by CYP3A4; undergoes sulfation and glucuronidation. Norethindrone acetate: hydrolyzed to norethindrone, then metabolized by reduction and glucuronidation.
Approximately 55% renal (30% as unchanged drug, 25% as metabolites) and 45% fecal (via biliary elimination).
Renal: ~40% as metabolites; fecal: ~30% (biliary); remainder as conjugates.
99% bound to albumin; minor binding to alpha-1-acid glycoprotein.
Ethinyl estradiol: 97-98% bound to albumin and SHBG; norethindrone acetate: 91-95% bound to albumin and SHBG.
0.27 L/kg (range 0.2-0.5 L/kg); distribution into total body water and highly perfused tissues.
Ethinyl estradiol: 2.3-3.6 L/kg; norethindrone acetate: 1.5-2.5 L/kg. Indicates extensive tissue distribution.
Oral: 85-90% (complete absorption; first-pass metabolism reduces systemic availability to ~75% in elderly).
Oral: Ethinyl estradiol ~45% (first-pass metabolism); norethindrone acetate ~64%.
No dose adjustment required for mild to moderate renal impairment. Not studied in severe renal impairment or end-stage renal disease; use with caution and monitor for adverse effects.
No dose adjustment is recommended for patients with mild to moderate renal impairment. Use is contraindicated in patients with severely impaired renal function (GFR <30 m L/min/1.73 m²) due to potential for fluid retention and hyperkalemia.
Contraindicated in acute hepatic disease or severe hepatic impairment (Child-Pugh class B or C). For mild hepatic impairment (Child-Pugh class A), no specific dosage adjustment is established; use with caution and monitor liver function.
Contraindicated in patients with acute or chronic hepatic dysfunction (Child-Pugh class B or C). For mild hepatic impairment (Child-Pugh class A), use with caution and monitor liver function; no specific dose adjustment guidelines are established.
Not indicated for use before menarche. For postmenarchal adolescents, same dosing as adults (one tablet daily as per 21/7 regimen).
Safety and efficacy have not been established in pediatric patients below 16 years of age. Post-pubertal adolescents may be dosed as adults, with careful consideration of risks (e.g., bone density).
Not indicated for use after menopause. No specific elderly considerations as the drug is not used in this population.
Not indicated for use in women over 65 years due to lack of efficacy and safety data, and increased risk of cardiovascular and thrombotic events.
Cigarette smoking increases risk of serious cardiovascular events from combination hormonal contraceptive use. Risk increases with age (>35 years) and with number of cigarettes smoked. Women over 35 who smoke should not use Kariva.
Cigarette smoking increases risk of serious cardiovascular events from combination oral contraceptives. Risk increases with age and smoking intensity (especially >35 years). Women >35 years who smoke should not use this product.
Increased risk of thromboembolic disorders (e.g., DVT, PE, MI, stroke),Hepatic neoplasia (benign and malignant) reported,Elevated blood pressure,Gallbladder disease,Carbohydrate and lipid metabolism effects,Retinal thrombosis (discontinue if vision loss or proptosis occurs),Depression,Bleeding irregularities (breakthrough bleeding, amenorrhea),Liver function abnormalities (discontinue if jaundice develops),Chloasma (may persist)
Thromboembolic disorders, cardiovascular disease (MI, stroke), hypertension, gallbladder disease, hepatic neoplasia, lipid effects, glucose intolerance, headache, breakthrough bleeding, depression, contact lens intolerance, fluid retention, hereditary angioedema.
Thrombophlebitis or thromboembolic disorders (current or history),Cerebrovascular or coronary artery disease,Known or suspected breast carcinoma,Endometrial carcinoma or other estrogen-dependent neoplasia,Undiagnosed abnormal genital bleeding,Pregnancy (known or suspected),Active liver disease or benign/malignant liver tumors,Severe hypertension,Diabetes with vascular involvement,Migraine with focal aura (especially if over 35 years),Hypersensitivity to any component,Use with Hepatitis C drug combinations containing ombitasvir/paritaprevir/ritonavir ± dasabuvir
Thrombophlebitis or thromboembolic disorders, cerebrovascular or coronary artery disease, known or suspected breast carcinoma, endometrial carcinoma or other estrogen-dependent neoplasia, undiagnosed abnormal genital bleeding, cholestatic jaundice of pregnancy or jaundice with prior pill use, hepatic adenoma or carcinoma, pregnancy, hypersensitivity to any component.
No specific food interactions; however, grapefruit juice may increase estrogen levels (theoretical). Avoid high-fat meals as they may affect absorption. Consistent intake with food can reduce nausea.
No specific food interactions are reported for Estrostep Fe. Grapefruit juice may slightly increase estrogen levels but is not considered clinically significant. There are no dietary restrictions. However, patients should maintain a consistent intake of folic acid if planning pregnancy; iron supplements can be taken with food to reduce GI upset.
FDA Pregnancy Category X. Contraindicated in pregnancy due to known teratogenicity. First trimester exposure associated with cardiovascular defects, limb reduction defects, and neural tube defects. Second and third trimester use linked to fetal hepatic adenoma and female pseudohermaphroditism (due to progestogenic activity).
Category X. Estrostep FE (norethindrone acetate/ethinyl estradiol/ferrous fumarate) is contraindicated in pregnancy. First trimester: increased risk of neural tube defects, cardiovascular anomalies, and limb reduction defects from sex hormones. Second/third trimester: feminization of male fetus, potential for urogenital malformations, and long-term reproductive tract effects. Postnatal: possible increased risk of childhood cancers.
Excreted into breast milk. M/P ratio not established. Avoid breastfeeding due to potential adverse effects in nursing infants.
Excreted in breast milk in small amounts (estrogen M/P ratio ~0.2, progestin M/P ratio ~0.6). May reduce milk quantity and quality. Use caution; generally not recommended. No adverse effects reported in infants at typical doses.
Not applicable; contraindicated in pregnancy. No dose adjustment recommended for use in non-pregnant women.
Contraindicated; no dose adjustment needed because drug should be discontinued immediately if pregnancy occurs. Pharmacokinetic changes in pregnancy (increased clearance, volume of distribution) not applicable due to contraindication.
Kariva (desogestrel/ethinyl estradiol) is a monophasic oral contraceptive. It is effective for contraception but also used for acne and menstrual regulation. Breakthrough bleeding is common in first 3 cycles. Counsel on missed pill protocol. Check for contraindications: smoking >35, history of DVT/PE, migraine with aura, liver disease, breast cancer. Note that antibiotics (rifampin, griseofulvin) and anticonvulsants may reduce efficacy.
Estrostep Fe is a combined oral contraceptive containing norethindrone acetate and ethinyl estradiol. It is unique among OCPs for its step-up estrogen regimen (20, 30, 35 mcg EE) intended to mimic natural menstrual cycle. Clinicians should note that it is not FDA-approved for acne treatment, though it is often used off-label; only Estrostep (non-Fe) is approved for acne. The iron (ferrous fumarate) in the last 7 tablets is a placebo. It is a low-dose pill; missed doses more likely cause breakthrough bleeding. Contraindications include smoking >35, history of DVT/PE, migraine with aura, liver disease, breast cancer. Counsel patients to take at same time daily; if missed, follow standard missed pill protocol.
Take one pill daily at the same time, preferably after an evening meal.,If you miss one pill, take it as soon as remembered; if missed two or more, use backup contraception.,Common side effects include nausea, breast tenderness, and spotting; these usually improve after 3 months.,Avoid smoking while taking this medication, especially if over 35 years old.,Inform your doctor before starting any new medications, including antibiotics and herbal supplements.,Kariva may decrease milk supply; not recommended if breastfeeding.
Take one pill at the same time each day. The first 21 pills contain active hormones; the last 7 pills are iron tablets (not hormones).,If you miss a pill, refer to the package insert or contact your healthcare provider. Use backup contraception (condoms) if pills are missed.,Common side effects include nausea, breast tenderness, headache, and breakthrough bleeding, especially in the first few months.,Estrostep Fe does not protect against sexually transmitted infections (STIs). Always use condoms for STI prevention.,Smoking while using this pill increases risk of serious cardiovascular events. Do not smoke.,Contact your doctor if you experience signs of a blood clot: sudden leg pain/swelling, chest pain, shortness of breath, or sudden severe headache.,The iron in the last 7 pills is to help with iron levels but does not provide hormonal contraception during that week.
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 KARIVA vs ESTROSTEP FE, answered by our medical review team.
KARIVA is a Combined Oral Contraceptive that works by Combination of ethinyl estradiol (estrogen) and levonorgestrel (progestin) that inhibits gonadotropin release, suppressing ovulation, altering cervical mucus to impede sperm penetration, and changing endometrial receptivity.. ESTROSTEP FE is a Combined Oral Contraceptive that works by Combination estrogen-progestin contraceptive: ethinyl estradiol suppresses gonadotropin release via negative feedback on hypothalamic-pituitary axis; norethindrone acetate produces progestational effects including endometrial transformation and cervical mucus thickening, inhibiting sperm penetration and implantation.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between KARIVA and ESTROSTEP FE depend on the specific clinical indication. These are both Combined Oral Contraceptive agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of KARIVA is: One tablet (0.15 mg levonorgestrel/0.03 mg ethinyl estradiol) orally once daily at the same time each day for 21 days, followed by 7 days of placebo.. The standard adult dose of ESTROSTEP FE is: One tablet daily orally, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg (24 active tablets) followed by ferrous fumarate 75 mg tablets (4 placebo tablets).. 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 KARIVA and ESTROSTEP FE 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. KARIVA is classified as Category C. FDA Pregnancy Category X. Contraindicated in pregnancy due to known teratogenicity. First trimester exposure associated with cardiovascular defects, limb reduction defects, and neu. ESTROSTEP FE is classified as Category C. Category X. Estrostep FE (norethindrone acetate/ethinyl estradiol/ferrous fumarate) is contraindicated in pregnancy. First trimester: increased risk of neural tube defects, cardiov. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.