Commentary| Volume 94, ISSUE 2, P104-108, August 2016

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The elusive minimum threshold concentration of levonorgestrel for contraceptive efficacy

      Progestins, either alone or in combination with ethinyl estradiol (EE), are a critical component of hormonal contraceptives. Levonorgestrel (LNG) has been extensively studied over decades and is considered to be a safe and highly effective progestin [
      • Ellertson C.
      History and efficacy of emergency contraception: beyond coca-cola. Journal [serial on the Internet].
      ]. However, the minimum threshold level of circulating LNG required for contraceptive efficacy is still uncertain.
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