When can a woman resume or initiate contraception after taking emergency contraceptive pills? A systematic review

Background: Hormonal emergency contraception can postpone ovulation, making a woman vulnerable to pregnancy later in the same cycle. However, concern exists as to whether concurrently administered emergency contraception pills (ECP) and other hormonal methods of contraception may affect the effectiveness of both medications. Study Design: A systematic review of the literature using PubMed and the Cochrane databases was performed to identify articles concerning the resumption or initiation of regular contraception within the same cycle as ECP use. We searched for articles in any language, published between 1980 and April 2012 and included all methods of emergency contraception pills available in the USA. Results: The search strategy identified 184 articles in the PubMed and Cochrane databases, of which none met inclusion criteria. Conclusion: The drug manufacturer advises continuation or initiation of routine contraception as soon as possible after use of ulipristal acetate, with concomitant use of a reliable barrier method until next menses. However, a theoretical concern exists that given ulipristal acetate's function as a selective progesterone receptor modulator, coadministration of a progestin could decrease its effectiveness as an emergency contraceptive. Initiation of hormonal contraception following levonorgestrel or the Yuzpe regimen for emergency contraception carries no similar concern for decreased method effectiveness.