Short answer: In the label's 13-week trial, common Femring side effects included headache, bleeding between periods (9.8% on 0.10 mg/day vs 1.9% on placebo), vaginal yeast infection (10.7% vs 2.8%), breast tenderness (10.7% vs 1.9%), back pain and bloating. Ring-related reports include toxic shock syndrome, the ring sticking to the vaginal or bladder wall, and placement into the bladder. Femring carries the estrogen boxed warning.
What Femring is approved for: Femring is a soft vaginal ring that releases estradiol at a rate equivalent to 0.05 mg or 0.10 mg per day for 3 months. It is approved to treat moderate to severe hot flashes (vasomotor symptoms) and moderate to severe vulvar and vaginal atrophy due to menopause (sections 1.1, 1.2, 3).
Source
FEMRING (estradiol acetate vaginal ring) prescribing information and Patient Information. Millicent US. DailyMed, version published December 19, 2025. DailyMed setid 7aaa97f9-a9d1-c815-e053-2991aa0afb9e
WARNING: ENDOMETRIAL CANCER, CARDIOVASCULAR DISORDERS, BREAST CANCER AND PROBABLE DEMENTIA
Estrogen-alone therapy: a woman with a uterus who uses estrogen without a progestin has a higher risk of endometrial cancer; adding a progestin lowers the risk of endometrial hyperplasia, a possible precursor. Undiagnosed persistent or recurring abnormal genital bleeding after menopause is checked, including with endometrial sampling when indicated. In the Women's Health Initiative (WHI), daily oral conjugated estrogens (CE) 0.625 mg alone raised the risk of stroke and deep vein thrombosis in women 50 to 79 over 7.1 years, and probable dementia in women 65 and older over 5.2 years. Estrogen plus progestin therapy: CE 0.625 mg plus medroxyprogesterone acetate 2.5 mg raised the risk of deep vein thrombosis, pulmonary embolism, stroke, heart attack, invasive breast cancer, and probable dementia in women 65 and older. Neither is to be used to prevent heart disease or dementia. Without comparable data, the label says these risks should be assumed to be similar for other doses and dosage forms. Estrogens are prescribed at the lowest effective dose for the shortest duration consistent with treatment goals and risks.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Femring.
| Adverse reaction | Placebo (n=108) | Femring 0.05 mg/day (n=113) | Femring 0.10 mg/day (n=112) |
|---|---|---|---|
| Headache (NOS) | 10 (9.3) | 8 (7.1) | 11 (9.8) |
| Intermenstrual bleeding | 2 (1.9) | 9 (8.0) | 11 (9.8) |
| Vaginal candidiasis | 3 (2.8) | 7 (6.2) | 12 (10.7) |
| Breast tenderness | 2 (1.9) | 7 (6.2) | 12 (10.7) |
| Back pain | 4 (3.7) | 7 (6.2) | 4 (3.6) |
| Abdominal distension | 3 (2.8) | 8 (7.1) | 3 (2.7) |
| Sinusitis (NOS) | 2 (1.9) | 2 (1.8) | 4 (3.6) |
| Uterine pain | 1 (0.9) | 2 (1.8) | 5 (4.5) |
| Urinary tract infection (NOS) | 2 (1.9) | 1 (0.9) | 4 (3.6) |
13-week trial of 225 postmenopausal women on Femring and 108 on placebo rings. Values are number of women (percent).
At week 12, moderate to severe hot flashes per week fell by a mean of 58.36 on 0.05 mg/day and 66.87 on 0.10 mg/day, vs 41.41 on placebo, from group baselines of 73.83, 75.11 and 83.62 per week (Table 3).
At week 13, vaginal superficial cells rose by a mean of 16.0 percent on 0.05 mg/day and 18.9 percent on 0.10 mg/day vs 1.11 percent on placebo; vaginal pH fell by 0.73 and 0.60 vs 0.25.
Average serum estradiol was 40.6 pg/mL on 0.05 mg/day and 76 pg/mL on 0.10 mg/day. Estradiol peaks about 1 hour after insertion, declines over the first 24 to 48 hours, then falls at a fairly steady rate for the rest of the 3 months.
Reported with vaginal rings: a few cases of toxic shock syndrome, ring adherence to the vaginal or bladder wall (some needing surgery), bowel obstruction, and ring insertion into the urinary bladder. Also reported after approval: uterine cancer, breast cancer, stroke, pulmonary embolism, pancreatitis, blindness, angioedema and anaphylaxis.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not use it. Women with undiagnosed abnormal genital bleeding, known, suspected or past breast cancer, estrogen-dependent cancer, current or past DVT, pulmonary embolism, stroke or heart attack, a known anaphylactic reaction or angioedema to Femring, liver impairment or disease, protein C, protein S or antithrombin deficiency or other clotting disorders, or known or suspected pregnancy.
Blood clots, stroke and heart attack. Estrogen alone raised stroke and DVT risk in the WHI; estrogen plus progestin raised pulmonary embolism, DVT, stroke and heart attack risk. Treatment is stopped right away if one occurs or is suspected and, if feasible, 4 to 6 weeks before surgery linked to clots or during long immobilization.
Endometrial, breast and ovarian cancer. Estrogen alone raises endometrial cancer risk in women with a uterus; adding a progestin lowers hyperplasia risk. The WHI found more invasive breast cancer on estrogen plus progestin, and hormone therapy has been linked to more abnormal mammograms and to ovarian cancer.
Probable dementia. In WHIMS studies of women 65 to 79, probable dementia was more common on CE alone and on CE plus MPA than on placebo. Whether this applies to younger women is unknown.
Vaginal use and expulsion. Femring may not suit women whose vagina is more prone to irritation, ulcers or expulsion, such as with a narrow vagina, vaginal stenosis, vaginal infection, cervical prolapse, rectocele or cystocele. If a vaginal infection needs local treatment, Femring can stay in place.
Ring-related problems. Toxic shock syndrome has been reported with vaginal rings. Rings have stuck to the vaginal or bladder wall, been placed into the bladder by mistake, and been linked to bowel obstruction; some cases needed surgical removal. If ulceration or erosion occurs, the ring may be left out until healing is complete.
Gallbladder, blood pressure and other conditions. Estrogens are linked to gallbladder disease needing surgery, high calcium in breast cancer spread to bone, retinal blood clots, raised blood pressure, high triglycerides with pancreatitis, thyroid changes and fluid retention, and can worsen endometriosis, hereditary angioedema, asthma, diabetes, epilepsy, migraine, porphyria and lupus (sections 5.4 to 5.16).
From the Patient Information that comes with Femring:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.