Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CYCLAFEM 0.5/35 vs ALYACEN 1/35
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Combination oral contraceptive containing norethindrone (progestin) and ethinyl estradiol (estrogen). Inhibits gonadotropin release, suppressing ovulation. Increases cervical mucus viscosity and alters endometrium, reducing sperm penetration and implantation.
Combination hormonal contraceptive: ethinyl estradiol suppresses gonadotropin release via negative feedback on hypothalamic-pituitary axis; norethindrone induces progestational effects including cervical mucus thickening and endometrial changes, inhibiting ovulation and sperm penetration.
Prevention of pregnancy,Treatment of moderate acne vulgaris in females ≥15 years,Oral contraceptive
Prevention of pregnancy
One tablet (0.5 mg norethindrone/35 mcg ethinyl estradiol) orally once daily for 21 days, followed by 7 placebo days (or no tablets) per cycle.
One tablet (norethindrone 1 mg and ethinyl estradiol 35 mcg) orally once daily for 21 consecutive days, followed by 7 days of placebo or no tablets.
Terminal elimination half-life of norethindrone is 5-14 hours (mean 7.6 hours); ethinyl estradiol half-life is 7-20 hours (mean ~13 hours). Steady-state is achieved within 5-7 days.
Norethindrone: 8-11 hours (terminal); ethinyl estradiol: 10-20 hours (terminal). The half-life supports once-daily dosing for oral contraceptive efficacy.
Norethindrone undergoes hepatic metabolism via reduction and hydroxylation followed by glucuronidation; ethinyl estradiol is metabolized primarily by CYP3A4 and undergoes first-pass metabolism with sulfation and glucuronidation in the gut wall and liver.
Ethinyl estradiol: primarily hepatic via CYP3A4; norethindrone: hepatic reduction and sulfate conjugation.
Renal excretion accounts for approximately 50-60% of the dose (as metabolites), with 30-40% excreted in feces via biliary elimination. Unchanged drug is minimal in urine.
Renal excretion of metabolites (primarily ethinyl estradiol and norethindrone conjugates) accounts for approximately 50-60% of elimination; fecal excretion accounts for 30-40%. Unchanged drug excretion is minimal (<5%).
Norethindrone: ~97% bound to albumin and SHBG. Ethinyl estradiol: ~98% bound to albumin.
Norethindrone: 61% bound to albumin and SHBG; ethinyl estradiol: 97-98% bound to albumin.
Norethindrone: Vd ~4 L/kg (total body water and tissue distribution). Ethinyl estradiol: Vd ~2.5 L/kg.
Norethindrone: 3.8-4.5 L/kg; ethinyl estradiol: 2.0-4.0 L/kg. Large Vd indicates extensive tissue distribution.
Oral bioavailability: norethindrone ~64% (due to first-pass metabolism); ethinyl estradiol ~45% (range 38-55%).
Oral: Norethindrone ~64%, ethinyl estradiol ~38-48% (due to first-pass metabolism).
No specific dosage adjustment required for mild to moderate renal impairment. Contraindicated in severe renal impairment or acute renal failure due to potential adverse effects on renal function and hormonal balance.
No dose adjustment required for mild to moderate renal impairment. Contraindicated in severe renal impairment or acute renal failure due to potential fluid retention and electrolyte disturbances.
Contraindicated in Child-Pugh class B and C (moderate to severe hepatic impairment). For mild hepatic impairment (Child-Pugh class A), use with caution; no specific dose adjustment but monitor liver function tests.
Contraindicated in patients with hepatic impairment, including Child-Pugh class B or C, due to impaired metabolism of estrogen and progestin. Not recommended in patients with active liver disease or history of liver tumors.
Not indicated for use before menarche. Post-menarche: same as adult dosing (one tablet daily per cycle) following standard contraceptive guidelines for adolescents.
Not indicated for use before menarche. For postmenarchal adolescents, same dosing as adults. Safety and efficacy established for contraception; weight-based dosing not applicable.
Not indicated for use in postmenopausal women due to lack of contraceptive need and increased risk of cardiovascular events and thromboembolism with estrogen-containing contraceptives.
Not indicated for use after menopause due to lack of benefit and increased risks (e.g., cardiovascular, thromboembolic events). If used, monitor for fluid retention, hypertension, and glucose intolerance.
Cigarette smoking increases risk of serious cardiovascular events from combination oral contraceptives. Risk increases with age and with heavy smoking (≥15 cigarettes/day). Women over 35 who smoke should not use this product.
Cigarette smoking increases risk of serious cardiovascular events from combined oral contraceptives. Risk increases with age and heavy smoking (≥15 cigarettes/day). Women over 35 who smoke should not use this product.
Increased risk of thromboembolic disorders (e.g., stroke, MI, DVT, PE),Increased risk of hepatic neoplasia (benign and malignant),Elevated blood pressure,Gallbladder disease,Carbohydrate and lipid metabolism effects,Ocular changes (retinal thrombosis),Depression,Headache/migraine,Hereditary angioedema exacerbation,Chloasma,Hepatic impairment,Pregnancy discontinuation,Lactation use
Thrombotic disorders (e.g., DVT, PE, stroke, MI),Cerebrovascular disease,Hepatic neoplasia,Gallbladder disease,Hypertension,Carbohydrate and lipid effects,Ocular lesions,Hereditary angioedema,Chloasma,Menstrual irregularities,Pregnancy exclusion prior to initiation
Thrombophlebitis or thromboembolic disorders (current or history),Cerebrovascular or coronary artery disease,Known or suspected breast carcinoma,Endometrial carcinoma or other estrogen-sensitive neoplasia,Undiagnosed abnormal genital bleeding,Cholestatic jaundice of pregnancy or jaundice with prior pill use,Hepatic adenoma or carcinoma,Known or suspected pregnancy,Hypersensitivity to any component,Age >35 and smoking ≥15 cigarettes/day
Venous or arterial thrombotic/thromboembolic disease (current or history),Cerebrovascular disease,Coronary artery disease,Known or suspected breast cancer,Endometrial or other estrogen-dependent neoplasia,Undiagnosed abnormal genital bleeding,Cholestatic jaundice of pregnancy or jaundice with prior pill use,Hepatic adenoma or carcinoma,Known or suspected pregnancy,Hypersensitivity to any component,Smoking in women over 35
No specific food restrictions. Grapefruit juice may slightly increase estrogen levels but not clinically significant. Maintain a balanced diet for overall health.
No significant food interactions. Grapefruit juice may increase estrogen levels, but clinically not a concern. Avoid excessive alcohol, which may impair liver function and increase estrogen exposure. Maintain a healthy diet, as weight gain is possible.
FIRST TRIMESTER: Increased risk of neural tube defects, cardiovascular malformations, and orofacial clefts with inadvertent exposure; absolute risk estimated at 3-4% above baseline. SECOND TRIMESTER: No direct teratogenic risk, but continue to avoid use due to hormonal effects. THIRD TRIMESTER: Potential for adverse fetal outcomes including respiratory distress, neonatal jaundice, and hypoglycemia; use contraindicated throughout pregnancy.
Pregnancy category X. Use of ALYACEN 1/35 (norethindrone/ethinyl estradiol) is contraindicated during pregnancy. First trimester: Increased risk of congenital anomalies, including cardiovascular defects and limb reduction defects. Second/third trimesters: Potential for urogenital abnormalities and feminization of male fetus. Exposure is associated with subsequent development of clear cell adenocarcinoma of vagina/cervix in female offspring (DES-related).
Contraindicated in breastfeeding. Estrogen and progestin are excreted in breast milk; M/P ratio unknown. May reduce milk production and alter milk composition. Theoretical risk of adverse effects in nursing infant. Alternative contraception recommended.
Small amounts of contraceptive steroids and/or metabolites have been identified in breast milk. M/P ratio: Not specifically determined for this combination; ethinyl estradiol M/P ratio ~0.02-0.04. Use may reduce milk production and quality. Breastfeeding not recommended during use. Alternative contraception advised.
Not applicable; drug is contraindicated in pregnancy. No dose adjustment recommended as use should be discontinued immediately upon confirmed pregnancy.
Contraindicated in pregnancy; no dose adjustments applicable. Discontinue medication immediately upon pregnancy detection.
CYCLAFEM 0.5/35 (norethindrone 0.5 mg/ethinyl estradiol 35 mcg) is a monophasic combination oral contraceptive. The 0.5 mg norethindrone dose is lower than typical progestin doses, reducing androgenic side effects. Its lower estrogen content (35 mcg) still provides effective cycle control. It is a first-line option for patients desiring contraception with minimal hormonal exposure. Breakthrough bleeding may occur in the first few cycles, especially with missed pills. Contraindicated in patients with migraine with aura, thrombophilia, or history of estrogen-dependent neoplasia.
ALYACEN 1/35 is a combination oral contraceptive containing ethinyl estradiol 35 mcg and norgestimate 1 mg. It is indicated for the prevention of pregnancy and for the treatment of moderate acne vulgaris in females ≥15 years of age who desire an oral contraceptive. Monitor for thromboembolic events, especially in smokers over 35 or those with migraine with aura. Use with caution in patients with liver impairment or history of cholestatic jaundice. The pill-free interval should not exceed 7 days; missed pills increase ovulation risk. Consider non-hormonal backup if vomiting or diarrhea occurs within 4 hours of dosing.
Take one tablet daily at the same time each day, with or without food.,If you miss a pill, refer to the package insert instructions; use backup contraception if needed.,Side effects may include nausea, breast tenderness, or spotting, especially during the first few months.,Smoking increases risk of serious cardiovascular events while on this medication; avoid smoking.,This medication does not protect against sexually transmitted infections (STIs); use condoms for STI prevention.,Notify your healthcare provider before starting new medications, as some (e.g., rifampin, certain anticonvulsants) may reduce effectiveness.,Store at room temperature, away from moisture and heat.
Take one tablet daily at the same time each day; do not skip doses.,Use an additional non-hormonal contraceptive (e.g., condoms) if you miss a pill, have vomiting, or diarrhea.,Smoking while on this pill increases the risk of blood clots and stroke, especially if you are over 35.,Contact your healthcare provider immediately if you have chest pain, leg pain/swelling, sudden vision changes, or severe headache.,This medication does not protect against HIV or other sexually transmitted infections.,Store at room temperature, away from moisture and heat.
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 CYCLAFEM 0.5/35 vs ALYACEN 1/35, answered by our medical review team.
CYCLAFEM 0.5/35 is a Oral Contraceptive that works by Combination oral contraceptive containing norethindrone (progestin) and ethinyl estradiol (estrogen). Inhibits gonadotropin release, suppressing ovulation. Increases cervical mucus viscosity and alters endometrium, reducing sperm penetration and implantation.. ALYACEN 1/35 is a Oral Contraceptive that works by Combination hormonal contraceptive: ethinyl estradiol suppresses gonadotropin release via negative feedback on hypothalamic-pituitary axis; norethindrone induces progestational effects including cervical mucus thickening and endometrial changes, inhibiting ovulation and sperm penetration.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CYCLAFEM 0.5/35 and ALYACEN 1/35 depend on the specific clinical indication. These are both 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 CYCLAFEM 0.5/35 is: One tablet (0.5 mg norethindrone/35 mcg ethinyl estradiol) orally once daily for 21 days, followed by 7 placebo days (or no tablets) per cycle.. The standard adult dose of ALYACEN 1/35 is: One tablet (norethindrone 1 mg and ethinyl estradiol 35 mcg) orally once daily for 21 consecutive days, followed by 7 days of placebo or no 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 CYCLAFEM 0.5/35 and ALYACEN 1/35 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. CYCLAFEM 0.5/35 is classified as Category C. FIRST TRIMESTER: Increased risk of neural tube defects, cardiovascular malformations, and orofacial clefts with inadvertent exposure; absolute risk estimated at 3-4% above baseline. ALYACEN 1/35 is classified as Category C. Pregnancy category X. Use of ALYACEN 1/35 (norethindrone/ethinyl estradiol) is contraindicated during pregnancy. First trimester: Increased risk of congenital anomalies, including . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.