The debate over conscience rights and emergency contraceptive agents among pharmacists and other healthcare professionals centers on the potential abortifacient potential of such agents. Such an important ethical and scientific question should be guided by established facts. This paper reviews the available evidence for post-fertilization effects of the emergency contraception drug levonorgestrel, and demonstrates that such evidence is uniformly lacking. The authors then discuss the ethical implications of these findings. This lack of any substantial evidence for post-fertilization effects may significantly weaken conscience claims, and may militate against refusals to dispense or to refer.