<p>The notion of placebo effect plays an important role in medicine, yet there is no widely accepted characterization of it. This paper defends and refines the view, originating with psychiatrist Arthur Shapiro, that placebo effects are characterized by their non-specificity. Although once influential, Shapiro’s view has faced strong criticism and has largely fallen out of favor. I argue, however, that there are two important and defensible senses in which placebo effects are non-specific, both of which can be made precise within Woodward’s interventionist framework of causation. First, placebo effects lack one–one specificity: when a treatment produces a response via the placebo effect, countless other treatments could produce the same outcome, and the treatment could easily produce many different outcomes. Second, the outcome of a placebo effect cannot be attributed specifically to the treatment itself; instead, patient expectations and conditioning history are the more important causes of the outcome. Drawing on the interventionist account of the dimensions that influence our judgments of causal importance, I show that placebos count as mere background conditions of the responses they provoke because of the non-specificity of their effects and their failure to meet closely related interventionist conditions of proportionality and stability. Properly articulated, the non-specificity account of placebo effects has substantial conceptual advantages and fares better than competing views in multiple respects.</p>