The slow spread of treatments supported by empirical evidence and the rapid diffusion of treatments lacking such support play major roles in the lower quality of mental health care received by people with severe mental illnesses compared with the care of less severely ill people. Further, the rapid spread of treatments that are of low cost-effectiveness limits the system's ability to provide the full gamut of high-value treatments available to treat this vulnerable population. Using the case of schizophrenia, we review the context in which these paradoxical patterns of diffusion have occurred, and we propose policy solutions.