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The most commonly used form of oral emergency contraception is a single 1.5-mg dose of levonorgestrel (brand name, Plan B), which disrupts ovulation and must be taken within 72 hours after unprotected sexual intercourse. Cyclo-oxygenase (COX) inhibitors — generally used as nonsteroidal anti-inflammatory drugs (NSAIDs) — also disrupt ovulation, but their ability to prevent pregnancy has not been studied previously.
Researchers in Hong Kong randomized 860 healthy women who requested emergency contraception to 1.5-mg levonorgestrel plus 40-mg piroxicam (a COX inhibitor with a half-life of ≈50 hours) or to levonorgestrel plus placebo. Mean time between unprotected sexual intercourse and emergency contraception use was 18 hours. Women using hormo…