Clinicians have good moral and professional reasons to contribute to pragmatic clinical trials (PCTs). We argue that clinicians have a defeasible duty to participate in this research that takes place in usual care settings and does not involve substantive deviation from their ordinary care practices. However, a variety of countervailing reasons may excuse clinicians from this duty in particular cases. Yet because there is a moral default in favor of participating, clinicians who wish to opt out of this research must (...) justify their refusal. Reasons to refuse include that the trial is badly designed in some way, that the trial activities will violate the clinician’s conscience, or that the trial will impose excessive burdens on the clinician. (shrink)