Estradiol sulfate
As the sodium salt, sodium estradiol sulfate, E2S is present as a minor constituent (0.9%) of conjugated equine estrogens (CEEs), or Premarin. It effectively functions as a prodrug to estradiol in this preparation, similarly to E1S. E2S is also formed as a metabolite of estradiol, as well as of estrone and E1S. Aside from its presence in CEEs, E2S is not available as a commercial pharmaceutical drug.
Estetrol/drospirenone
Estetrol/drospirenone (E4/DRSP; tentative brand name Estelle; developmental code name FSN-013) is a combination of estetrol, an estrogen, and drospirenone, a progestin, which is under development by Estetra S.A. as a combined oral contraceptive for the prevention of pregnancy in women. It contains 15 mg estetrol and 3 mg drospirenone. As of 2018, it is in phase III clinical trials for this indication.