This article examines the concept of assay sensitivity in clinical research. Defined as the ability of a clinical trial to distinguish between an effective and ineffective treatment, the need for assay sensitivity has been taken to support the claim that placebos are methodologically superior to active control treatments. The demands of doing good clinical science must trump the physician-researcher’s ethical duty to provide all trial participants with nothing less than competent medical care. We argue that this supposed implication of assay sensitivity rests on (1) collapsing the distinction between biological efficacy and clinical effectiveness, and (2) conflating the epistemic contexts of a trial-as-designed and a trial-as-executed. Once these errors are corrected, it becomes clear that placebos grant no epistemological advantage over active controls, and there is therefore no longer a tension between the epistemic and ethical demands of research. We suggest that the legitimate worries behind assay sensitivity can be better understood as the need for researchers to articulate their experimental heuristics and to demonstrate a robust pattern of evidence across a series of trials.