title: Emergency contraception with levonorgestrel: one hormone better than two.
authors.forename: P A
authors.initials: PA
authors.lastname: O'Brien
mesh_terms: D002626:Chemistry, Pharmaceutical; D003280:Contraceptives, Oral, Synthetic / Q000008:administration & dosage*; D003281:Contraceptives, Postcoital / Q000008:administration & dosage*; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D016912:Levonorgestrel / Q000008:administration & dosage*; D011247:Pregnancy; D018873:Pregnancy Rate; D011275:Pregnancy, Unwanted; D016032:Randomized Controlled Trials as Topic / Q000592:standards*
chemical_list: D003280:Contraceptives, Oral, Synthetic; D003281:Contraceptives, Postcoital; D016912:Levonorgestrel