Last reviewed 2026-04-20 · How we verify

Femring (ESTRADIOL ACETATE)

Estrogens, primarily estradiol, bind to nuclear receptors in estrogen-responsive tissues, modulating the female reproductive system and reducing postmenopausal gonadotropin levels.

Femring is a small molecule estrogen medication, originally developed by Warner Ireland and currently owned by Apil. It targets the estrogen receptor and is FDA-approved for the treatment of atrophic vaginitis since 2003. Femring is an off-patent medication with no active Orange Book patents, meaning it can be manufactured generically. However, there are currently no generic manufacturers available. As an estrogen medication, Femring carries key safety considerations, including potential risks of blood clots and endometrial cancer.

At a glance

Mechanism of action

Estrogens, mainly estradiol, play a crucial role in developing and maintaining the female reproductive system and secondary sexual characteristics. They achieve this by binding to nuclear receptors in various tissues, affecting gene expression and hormonal balance. In postmenopausal women, estrogens help reduce elevated levels of LH and FSH through a negative feedback mechanism.

Approved indications

• Atrophic vaginitis

Boxed warnings

• WARNING: ENDOMETRIAL CANCER, CARDIOVASCULAR DISORDERS, BREAST CANCER AND PROBABLE DEMENTIA Estrogen-Alone Therapy Endometrial Cancer There is an increased risk of endometrial cancer in a woman with a uterus who uses unopposed estrogens. Adding a progestin to estrogen therapy has been shown to reduce the risk of endometrial hyperplasia, which may be a precursor to endometrial cancer. Adequate diagnostic measures, including directed or random endometrial sampling when indicated, should be undertaken to rule out malignancy in postmenopausal women with undiagnosed persistent or recurring abnormal genital bleeding [see Warnings and Precautions (5.2) ] . Cardiovascular Disorders and Probable Dementia Estrogen-alone therapy should not be used for the prevention of cardiovascular disease or dementia [see Warnings and Precautions (5.1 , 5.3 ), and Clinical Studies (14.3 , 14.4 )] . The Women’s Health Initiative (WHI) estrogen-alone substudy reported increased risks of stroke and deep vein thrombosis (DVT) in postmenopausal women (50 to 79 years of age) during 7.1 years of treatment with daily oral conjugated estrogens (CE) [0.625 mg]-alone, relative to placebo [see Warnings and Precautions (5.1) , and Clinical Studies (14.3) ]. The WHI Memory Study (WHIMS) estrogen-alone ancillary study of the WHI reported an increased risk of developing probable dementia in postmenopausal women 65 years of age or older during 5.2 years of treatment with daily CE (0.625 mg)-alone, relative to placebo. It is unknown whether this finding applies to younger postmenopausal women [see Warnings and Precautions (5.3) , Use in Specific Populations (8.5) , and Clinical Studies (14.4) ]. In the absence of comparable data, these risks should be assumed to be similar for other doses of CE and other dosage forms of estrogens. Estrogens with or without progestins should be prescribed at the lowest effective doses and for the shortest duration consistent with treatment goals and risks for the individual woman. Estrogen Plus Progestin Therapy Cardiovascular Disorders and Probable Dementia Estrogen plus progestin therapy should not be used for the prevention of cardiovascular disease or dementia [see Warnings and Precautions (5.1 , 5.3 ) and Clinical Studies (14.3 , 14.4 )] . The WHI estrogen plus progestin substudy reported increased risks of DVT, pulmonary embolism (PE), stroke and myocardial infarction (MI) in postmenopausal women (50 to 79 years of age) during 5.6 years of treatment with daily oral CE (0.625 mg) combined with medroxyprogesterone acetate (MPA) [2.5 mg], relative to placebo [see Warnings and Precautions (5.1) , and Clinical Studies (14.3) ] . The WHIMS estrogen plus progestin ancillary study of the WHI reported increased risk of developing probable dementia in postmenopausal women 65 years of age or older during 4 years of treatment with daily CE (0.625 mg) combined with MPA (2.5 mg), relative to placebo. It is unknown whether this finding applies to younger postmenopausal women [see Warnings and Precautions (5.3) , Use in Specific Populations (8.5) and Clinical Studies (14.4) ] . Breast Cancer The WHI estrogen plus progestin substudy also demonstrated an increased risk of invasive breast cancer [see Warnings and Precautions (5.3) , and Clinical Studies (14.3) ]. In the absence of comparable data, these risks should be assumed to be similar for other doses of CE and MPA and other combinations and dosage forms of estrogens and progestins. Estrogens with or without progestins should be prescribed at the lowest effective doses and for the shortest duration consistent with treatment goals and risks for the individual woman. WARNING: ENDOMETRIAL CANCER, CARDIOVASCULAR DISORDERS, BREAST CANCER, AND PROBABLE DEMENTIA See full prescribing information for complete boxed warning. Estrogen-Alone Therapy • There is an increased risk of endometrial cancer in a woman with a uterus who uses unopposed estrogens ( 5.2 ) • Estrogen-alone therapy should not be used for the prevention of cardiovascular disease or dementia ( 5.1 , 5.3 ) • The Women’s Health Initiative (WHI) estrogen-alone substudy reported increased risks of stroke and deep vein thrombosis (DVT) ( 5.1 ) • The WHI Memory Study (WHIMS) estrogen-alone ancillary study of WHI reported an increased risk of probable dementia in postmenopausal women 65 years of age and older ( 5.3 ) Estrogen Plus Progestin Therapy • Estrogen plus progestin therapy should not be used for the prevention of cardiovascular disease or dementia ( 5.1 , 5.3 ) • The WHI estrogen plus progestin substudy reported increased risks of stroke, DVT, pulmonary embolism (PE), and myocardial infarction (MI) ( 5.1 ) • The WHI estrogen plus progestin substudy reported an increased risk of invasive breast cancer ( 5.2 ) • The WHIMS estrogen plus progestin ancillary study of WHI reported an increased risk of probable dementia in postmenopausal women 65 years of age and older ( 5.3 )

Common side effects

• Headache (NOS)
• Intermenstrual Bleeding
• Vaginal Candidiasis
• Breast Tenderness
• Back Pain
• Abdominal Distension
• Sinusitis (NOS)
• Uterine Pain
• Urinary Tract Infection (NOS)

Key clinical trials

• Menopausal Hormones and Sympathetic Activation (PHASE4)
• Capivasertib+Fulvestrant asTreatment for Locally Advanced(Inoperable) or Metastatic HR+/HER2- Breast Cancer in Chinese Patients (PHASE3)
• Targeted Therapy Directed by Genetic Testing in Treating Patients With Locally Advanced or Advanced Solid Tumors, The ComboMATCH Screening Trial (PHASE2)
• Romosozumab as an Adjunct to Physiologic Estrogen Replacement in Functional Hypothalamic Amenorrhea (PHASE3)
• Study of ECI830 Single Agent or in Combination in Patients With Advanced HR+/HER2- Breast Cancer and Other Advanced Solid Tumors (PHASE1,PHASE2)
• A Study of LOXO-783 in Patients With Breast Cancer/Other Solid Tumors (PHASE1)
• Efficacy and Safety of Tinengotinib Tablets Combined With Fulvestrant Injection in Patients With HR Positive and HER-2 Negative Recurrent or Metastatic Breast Cancer Who Have Failed Prior Treatment (PHASE2)
• Liquid-biopsy Informed Platform Trial to Evaluate CDK4/6-inhibitor Resistant ER+/HER2- Metastatic Breast Cancer (PHASE2)

Patents

Primary sources

Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.

Competitive intelligence

For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:

• Femring CI brief — competitive landscape report
• Femring updates RSS · CI watch RSS
• Apil portfolio CI