Short answer: Estring and Femring are both soft vaginal rings left in for 90 days.12 Estring releases about 7.5 mcg of estradiol a day and is approved only for vaginal atrophy. Femring releases 0.05 mg or 0.10 mg a day and is approved for hot flashes as well as vaginal atrophy. Femring carries the estrogen boxed warning; this Estring label version has none. Neither label reports a trial against the other.
| Estring | Femring | |
|---|---|---|
| Approved for | Moderate to severe vulvar and vaginal atrophy from menopause1 | Moderate to severe hot flashes and moderate to severe vulvar and vaginal atrophy from menopause2 |
| Estradiol released | About 7.5 mcg a day (2 mg estradiol per ring)1 | 0.05 mg or 0.10 mg a day (as estradiol acetate)2 |
| Wear time | Left in continuously for 3 months, then replaced if treatment continues1 | 90 days, then replaced if treatment continues2 |
| If it comes out | Rinse in lukewarm water and put it back1 | Clean with warm water and put it back2 |
| Side effects in label trials | Headache 13% vs 16% on vaginal cream; vaginal discharge 7% vs 3%1 | Breast tenderness 10.7% on 0.10 mg vs 1.9% on placebo; vaginal yeast infection 10.7% vs 2.8%2 |
| Boxed warning | None in this label version1 | Endometrial cancer, heart and stroke risk, breast cancer, probable dementia2 |
The two rings are made for different jobs. Estring holds 2 mg of estradiol and releases about 7.5 mcg a day to treat the vagina itself; its label says some estradiol is absorbed, though less than from estrogens used for hot flashes.1 Femring releases 0.05 mg or 0.10 mg a day, enough to be approved for hot flashes, and its label starts at 0.05 mg a day.2 Femring's label says a woman with a uterus should generally also be considered for a progestin.2
Both labels list reports of toxic shock syndrome and of the ring sticking to the vaginal wall, sometimes needing surgery to remove.12 Femring's label also lists the ring sticking to the bladder wall and being placed into the bladder by mistake.2 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Which ring, if any, fits is for your prescriber. More detail: Estring side effects, Femring side effects, the Estring and Femring dosing schedules, and the Vaginal Estradiol (Vagifem, Estrace cream) guide.