Editing Emergency contraception (section)

==Interactions==
The herbal preparation of [[Hypericum perforatum|St John's wort]] and some [[enzyme induction|enzyme-inducing]] drugs (e.g. [[anticonvulsant]]s or [[rifampicin]]) may reduce the effectiveness of ECP, and a larger dose may be required,<ref name="FSRH EC 2012">{{cite journal|author1=RCOG Faculty of Sexual |author2=Reproductive Healthcare |author3=Clinical Effectiveness Unit |date=January 2012|title=Clinical guidance: emergency contraception|journal=Clinical Guidance |location=London|publisher=Royal College of Obstetricians and Gynaecologists|issn=1755-103X|url=http://www.fsrh.org/pdfs/CEUguidanceEmergencyContraception11.pdf|access-date=2012-04-30}} p.3:{{blockquote|How does EC work?<br />In 2002, a judicial review ruled that pregnancy begins at implantation, not fertilisation.<sup>8</sup> The possible mechanisms of action should be explained to the patient as some methods may not be acceptable, depending on individual beliefs about the onset of pregnancy and abortion.<br />Copper-bearing intrauterine device (Cu-IUD). Copper is toxic to the ovum and sperm and thus the copper-bearing intrauterine device (Cu-IUD) is effective immediately after insertion and works primarily by inhibiting fertilisation.<sup>9–11</sup> A systematic review on mechanisms of action of IUDs showed that both pre- and postfertilisation effects contribute to efficacy.<sup>11</sup> If fertilisation has already occurred, it is accepted that there is an anti-implantation effect,<sup>12,13</sup><br />Levonorgestrel (LNG). The precise mode of action of levonorgestrel (LNG) is incompletely understood but it is thought to work primarily by inhibition of ovulation.<sup>16,17</sup><br />Ulipristal acetate (UPA). UPA's primary mechanism of action is thought to be inhibition or delay of ovulation.<sup>2</sup>}}</ref><ref name="FSRH DI 2012">{{cite journal|author1=RCOG Faculty of Sexual|author2=Reproductive Healthcare|author3=Clinical Effectiveness Unit|date=January 2012|title=Clinical guidance: drug interactions with hormonal contraception|journal=Clinical Guidance|location=London|publisher=Royal College of Obstetricians and Gynaecologists|issn=1755-103X|url=http://www.fsrh.org/pdfs/CEUguidancedruginteractionshormonal.pdf|access-date=2012-04-30|url-status=dead|archive-url=https://web.archive.org/web/20120526134911/http://www.fsrh.org/pdfs/CEUGuidanceDrugInteractionsHormonal.pdf|archive-date=2012-05-26}}</ref> especially in women who weigh more than 165&nbsp;lbs.<ref name=":1" />