This article examines traditions of testing drugs (as substances) and trying cures (on patients) in medieval and early modern Europe. It argues that the history of drug testing needs to be a more central story to overall histories of scientific experiment. The practice of conducting thoughtful—and sometimes contrived—tests on drugs has a rich and varied tradition dating back to antiquity, which expanded in the Middle Ages and early modern period. Learned physicians paired text-based knowledge (reason) with hands-on testing (experience or experiment) in order to make claims about drugs' properties or effects on humans. Lay practitioners similarly used hands-on testing to gain knowledge of pharmaceutical effects. Although drug testing practices expanded in scale, actors, and sites, therpublished a work extolling the virtues of drugs froe was significant continuity from the Middle Ages to the eighteenth century.