Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
GILDESS 24 FE 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 of ethinyl estradiol and drospirenone provides contraceptive effect primarily by suppression of gonadotropins (FSH and LH), inhibition of ovulation, and alterations in cervical mucus and endometrium. Drospirenone has antimineralocorticoid activity and antiandrogenic properties.
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 women at least 14 years old who have achieved menarche and desire contraception,Treatment of premenstrual dysphoric disorder (PMDD) in women who choose to use an oral contraceptive for contraception
Prevention of pregnancy
One tablet orally once daily for 24 days, followed by 4 days of placebo (iron tablets). The active tablets contain 0.8 mg norethindrone acetate and 0.025 mg ethinyl estradiol.
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.
Ethinyl estradiol: terminal half-life ~13-27 hours (mean ~17 hours); drospirenone: terminal half-life ~30-40 hours (mean ~32 hours). Clinical context: Steady-state achieved within 10 days for both components.
Norethindrone: 8-11 hours (terminal); ethinyl estradiol: 10-20 hours (terminal). The half-life supports once-daily dosing for oral contraceptive efficacy.
Primarily metabolized via CYP3A4; drospirenone is also metabolized via CYP3A4 and sulfation. Ethinyl estradiol undergoes first-pass metabolism and is conjugated in the gut and liver.
Ethinyl estradiol: primarily hepatic via CYP3A4; norethindrone: hepatic reduction and sulfate conjugation.
Renal: ~50-60% as metabolites (ethinyl estradiol glucuronide and sulfate conjugates, drospirenone metabolites); fecal: ~40-50% (drospirenone metabolites); biliary excretion contributes to enterohepatic circulation.
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%).
Ethinyl estradiol: ~98% bound (primarily albumin); drospirenone: ~95-97% bound (albumin and sex hormone-binding globulin, SHBG).
Norethindrone: 61% bound to albumin and SHBG; ethinyl estradiol: 97-98% bound to albumin.
Ethinyl estradiol: Vd ~2-4 L/kg (extensive tissue distribution); drospirenone: Vd ~4 L/kg (distributes to tissues, including breast and reproductive organs).
Norethindrone: 3.8-4.5 L/kg; ethinyl estradiol: 2.0-4.0 L/kg. Large Vd indicates extensive tissue distribution.
Oral: Ethinyl estradiol ~45-50% (first-pass metabolism); drospirenone ~76-85% (high oral bioavailability, limited first-pass effect).
Oral: Norethindrone ~64%, ethinyl estradiol ~38-48% (due to first-pass metabolism).
No dose adjustment required for mild to moderate renal impairment. Not studied in severe renal impairment; use with caution due to potential fluid retention and hormonal changes.
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 or C (moderate to severe hepatic impairment). For mild impairment (Child-Pugh A), no dose adjustment but monitor liver function.
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.
Safety and efficacy not established in postmenarcheal females less than 18 years of age. Use is generally not recommended before menarche.
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. No specific geriatric dosing; use is not recommended in this population.
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 the risk of serious cardiovascular events from combination oral contraceptive use. This risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over 35 years of age. Women who use combination oral contraceptives should be strongly advised not to smoke.
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.
Thrombotic and other vascular events (e.g., myocardial infarction, stroke, venous thromboembolism),Risk for hyperkalemia in patients with renal/hepatic impairment or on medications that increase potassium,Liver disease (e.g., acute hepatitis, cholestatic jaundice),Hypertension,Carbohydrate and lipid metabolic effects,Headache (including migraine),Bleeding irregularities,Depression,Gallbladder disease,Hereditary angioedema
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
Renal impairment (creatinine clearance <30 m L/min),Adrenal insufficiency,High risk of arterial/venous thrombotic events,Current or history of breast cancer or other estrogen-sensitive cancer,Liver tumors or active liver disease,Undiagnosed abnormal uterine bleeding,Pregnancy,Hypersensitivity to any component
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 significant food interactions. Grapefruit juice may increase estrogen levels, but clinical significance is low. Avoid St. John's wort as it can reduce contraceptive efficacy.
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.
FDA Pregnancy Category X. Contraindicated in pregnancy. First trimester: Increased risk of congenital anomalies (cardiovascular defects, neural tube defects) from estrogen/progestin exposure. Second/third trimester: No direct fetal toxicity reported. Postpartum: Excreted in breast milk, but no adverse effects documented.
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).
Safety category L3 (moderately safe). Ethinyl estradiol levels in milk: 0.8-1.5 ng/m L; M/P ratio ~0.3. Levonorgestrel levels: 0.5-1.0 ng/m L; M/P ratio ~0.4. Theoretical risk of estrogenic effects in infant; use alternative contraception if possible.
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.
Contraindicated in pregnancy. No dose adjustments required as drug should be discontinued immediately if pregnancy occurs. Pharmacokinetic changes (e.g., increased hepatic clearance, plasma volume expansion) are irrelevant due to contraindication.
Contraindicated in pregnancy; no dose adjustments applicable. Discontinue medication immediately upon pregnancy detection.
GILDESS 24 FE is a combined oral contraceptive containing ethinyl estradiol and desogestrel. Iron supplementation (ferrous fumarate) in the placebo pills may cause constipation or black stools. Monitor for thromboembolic events, especially in smokers over 35. Efficacy may be reduced with enzyme-inducing drugs. Missed pill protocol: if missed one active pill, take as soon as remembered; if missed two or more, take last missed pill and use backup contraception for 7 days.
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 pill daily at the same time, even if not sexually active.,If you miss a pill, refer to the package insert for instructions; use backup contraception if needed.,Iron pills in the placebo week may cause dark stools or constipation; inform your doctor if symptoms persist.,Do not smoke while taking this medication, especially if over 35, due to increased risk of blood clots.,Common side effects include nausea, breast tenderness, and breakthrough bleeding; these often improve after 3 months.,Seek immediate medical attention for signs of blood clot: leg pain/swelling, sudden chest pain, shortness of breath, or severe headache.
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 GILDESS 24 FE vs ALYACEN 1/35, answered by our medical review team.
GILDESS 24 FE is a Oral Contraceptive that works by Combination of ethinyl estradiol and drospirenone provides contraceptive effect primarily by suppression of gonadotropins (FSH and LH), inhibition of ovulation, and alterations in cervical mucus and endometrium. Drospirenone has antimineralocorticoid activity and antiandrogenic properties.. 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 GILDESS 24 FE 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 GILDESS 24 FE is: One tablet orally once daily for 24 days, followed by 4 days of placebo (iron tablets). The active tablets contain 0.8 mg norethindrone acetate and 0.025 mg ethinyl estradiol.. 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 GILDESS 24 FE 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. GILDESS 24 FE is classified as Category C. FDA Pregnancy Category X. Contraindicated in pregnancy. First trimester: Increased risk of congenital anomalies (cardiovascular defects, neural tube defects) from estrogen/progesti. 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.