On Thursday, the Food and Drug Administration made what may be the most momentous drug-approval decision in its history: It granted emergency-use authorization for Mercks molnupiravir to treat covid-19. This approval is significant not because molnupiravir is an especially good drug, but because it is a rather ineffective and dangerous one. In particular, molnupiravir might create new variants of SARS-CoV-2 that evade immunity and prolong the pandemic.