In the sixteenth century, a series of dramatic medical experiments on human subjects took place at the princely courts of Europe. Under the watch of learned physicians, condemned criminals would take poison, followed by a promising antidote. In several cases, physicians meticulously recorded and shared extensive descriptions of the tests. This book tells the forgotten story of these poison trials. It focuses on antidote tests both as a mirror of Renaissance medical practice and an important crucible for ideas about evidence, authority, and proof. At a time when poison was widely feared as a harming agent and as the root of deadly diseases like plague, the urgent need for effective cures provoked intense excitement about new antidotes. Many poison antidotes had long had a special status as near cure-alls, recommended as plague cures in particular. Antidotes thus played a central role in a broader fascination with new wonder drugs, both exotic substances encountered through trade and colonial expansion and local alchemical cures. The book makes three overarching arguments about experiment, authority, and medical ethics. Physicians cast poison trials as learned medical experiments, an explicit contrast to the marketplace theatrics of charlatans, who often performed dramatic shows with poisons and antidotes. At the same time, there were many limitations to using humans for deadly tests. Outside of the princely courts, physicians took ownership of antidote cure-alls by describing marvelous incidences of curing illness, while empirical practitioners, including alchemists, also tried to direct what kinds of evidence counted as valid proof.