Five study centers enrolled 1,311 women seeking postcoital contraception methods. Ethinyl estradiol was administered at 5 mg/day and conjugated estrogens at 30 mg/day for five consecutive days starting within 72 hours of unprotected coitus. Eleven pregnancies occurred in the 976 women who had a single unprotected coitus at midcycle. Based on published information, 69 pregnancies would have been expected if no contraceptives were used. Although both treatments were effective in preventing pregnancy, ethinyl estradiol seemed to be more effective. At the two centers alternately prescribing both drugs, none of 137 women treated with ethinyl estradiol became pregnant, while six of the 132 given conjugated estrogens became pregnant. Women whose treatment commenced on the first postcoital day seemed to have lower pregnancy rates than those whose medication was delayed to the second or third postcoital day regardless of which drug was used. Side effects were mainly limited to nausea that occurred in 70% and vomiting that was experienced by 33% of all women treated.
(JAMA 244:1336-1339, 1980)
Dixon GW, Schlesselman JJ, Ory HW, Blye RP. Ethinyl Estradiol and Conjugated Estrogens as Postcoital Contraceptives. JAMA. 1980;244(12):1336–1339. doi:10.1001/jama.1980.03310120024016