GYNODIOL

Clinical safety rating: caution

Comprehensive clinical and safety monograph for GYNODIOL (GYNODIOL).

How it works

Estradiol acts by binding to nuclear estrogen receptors, which modulate gene transcription and lead to the development and maintenance of female reproductive tissues and secondary sexual characteristics. Norethindrone acetate is a progestin that suppresses gonadotropin secretion and induces secretory changes in the endometrium.

What the body does with it

Metabolism	Estradiol is primarily metabolized in the liver via CYP3A4, with some involvement of CYP1A2 and CYP2C9, to estrone and estriol. Norethindrone acetate is metabolized in the liver via CYP3A4 to inactive metabolites.
Excretion	Renal 50-80% as metabolites and conjugates; biliary/fecal 10-20%; unchanged drug <5%.
Half-life	Terminal half-life approximately 24-30 hours; steady-state reached by 5-7 days.
Protein binding	97-99% bound to albumin and sex hormone-binding globulin (SHBG).
Volume of Distribution	0.7-1.0 L/kg; distributes into body water and adipose tissue.
Bioavailability	Oral: 40-60% due to first-pass metabolism.
Onset of Action	Oral: 2-4 hours to peak serum levels; clinical effects (e.g., menstrual regulation) within first cycle.
Duration of Action	Clinical effects persist for duration of treatment; hormonal suppression lasts 24-48 hours after last dose.

Classification & Brands

Dosing & administration

1 tablet (ethinylestradiol 0.035 mg/norethisterone 1 mg) orally once daily for 21 days, followed by 7 days of placebo or hormone-free interval.

Dosage form	TABLET
Renal impairment	No specific dose adjustment recommended for GFR >30 mL/min. Use contraindicated in severe renal impairment (GFR <30 mL/min) due to risk of fluid retention and hyperkalemia.
Liver impairment	Contraindicated in Child-Pugh class B or C (moderate to severe hepatic impairment). For Child-Pugh A: use with caution; no specific dose adjustment but monitor liver function.
Pediatric use	Not indicated for use before menarche. For post-menarche adolescents >12 years: same as adult dosing; 1 tablet daily for 21 days followed by 7-day break.
Geriatric use	Not indicated for postmenopausal women. No specific dose adjustment; use only if benefit outweighs cardiovascular and thromboembolic risks.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for GYNODIOL (GYNODIOL).

Breastfeeding	Estradiol is excreted into breast milk in low amounts (M/P ratio ~0.5-0.8). May decrease milk production and quality. Avoid use during breastfeeding unless essential. Consider alternative therapies.
Teratogenic Risk	GYNODIOL (estradiol valerate) is contraindicated in pregnancy. First trimester: Increased risk of congenital anomalies including cardiovascular and limb defects. Second and third trimesters: Fetal exposure may cause genitourinary tract abnormalities, feminization of male fetuses, and potential long-term reproductive effects. Use only if clearly needed for maternal condition.

Warnings & precautions

■ FDA Black Box Warning

Estrogens increase the risk of endometrial cancer. There is an increased risk of cardiovascular events and probable dementia in women >65 years. Do not use for prevention of cardiovascular disease.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Undiagnosed abnormal genital bleeding","Known or suspected pregnancy","Active or history of breast cancer","Active venous or arterial thromboembolism","Active or history of DVT/PE","Known thrombophilic disorders (e.g., Protein C, S, or antithrombin deficiency)","Known or suspected estrogen-dependent neoplasia","Severe hepatic impairment or liver disease (if transaminases not returned to normal)","Hypersensitivity to any component"]

Clinical Precautions

Precautions

["Cardiovascular disorders (e.g., stroke, DVT, pulmonary embolism)","Malignancies (e.g., breast cancer, endometrial cancer)","Dementia risk in women >65 years","Gallbladder disease","Hypertriglyceridemia","Fluid retention","Hepatic hemangiomas or liver disease","Hypocalcemia","Ocular abnormalities (e.g., retinal thrombosis)"]

Clinical Tips & Counseling

Drug interactions

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GYNODIOL

Clinical safety rating: caution

Comprehensive clinical and safety monograph for GYNODIOL (GYNODIOL).

How it works

What the body does with it

Metabolism	Estradiol is primarily metabolized in the liver via CYP3A4, with some involvement of CYP1A2 and CYP2C9, to estrone and estriol. Norethindrone acetate is metabolized in the liver via CYP3A4 to inactive metabolites.
Excretion	Renal 50-80% as metabolites and conjugates; biliary/fecal 10-20%; unchanged drug <5%.
Half-life	Terminal half-life approximately 24-30 hours; steady-state reached by 5-7 days.
Protein binding	97-99% bound to albumin and sex hormone-binding globulin (SHBG).
Volume of Distribution	0.7-1.0 L/kg; distributes into body water and adipose tissue.
Bioavailability	Oral: 40-60% due to first-pass metabolism.
Onset of Action	Oral: 2-4 hours to peak serum levels; clinical effects (e.g., menstrual regulation) within first cycle.
Duration of Action	Clinical effects persist for duration of treatment; hormonal suppression lasts 24-48 hours after last dose.

Classification & Brands

Dosing & administration

1 tablet (ethinylestradiol 0.035 mg/norethisterone 1 mg) orally once daily for 21 days, followed by 7 days of placebo or hormone-free interval.

Dosage form	TABLET
Renal impairment	No specific dose adjustment recommended for GFR >30 mL/min. Use contraindicated in severe renal impairment (GFR <30 mL/min) due to risk of fluid retention and hyperkalemia.
Liver impairment	Contraindicated in Child-Pugh class B or C (moderate to severe hepatic impairment). For Child-Pugh A: use with caution; no specific dose adjustment but monitor liver function.
Pediatric use	Not indicated for use before menarche. For post-menarche adolescents >12 years: same as adult dosing; 1 tablet daily for 21 days followed by 7-day break.
Geriatric use	Not indicated for postmenopausal women. No specific dose adjustment; use only if benefit outweighs cardiovascular and thromboembolic risks.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for GYNODIOL (GYNODIOL).

Breastfeeding	Estradiol is excreted into breast milk in low amounts (M/P ratio ~0.5-0.8). May decrease milk production and quality. Avoid use during breastfeeding unless essential. Consider alternative therapies.
Teratogenic Risk	GYNODIOL (estradiol valerate) is contraindicated in pregnancy. First trimester: Increased risk of congenital anomalies including cardiovascular and limb defects. Second and third trimesters: Fetal exposure may cause genitourinary tract abnormalities, feminization of male fetuses, and potential long-term reproductive effects. Use only if clearly needed for maternal condition.

Warnings & precautions

■ FDA Black Box Warning

Estrogens increase the risk of endometrial cancer. There is an increased risk of cardiovascular events and probable dementia in women >65 years. Do not use for prevention of cardiovascular disease.