The Obama administration has made a major investment in comparative effectiveness research (CER) to learn what treatments work best for which patients. CER has the potential to reduce wasteful medical spending and improve patient outcomes, but the political sustainability of this initiative remains unclear because of concerns that it will threaten the doctor-patient relationship. An unresolved question is whether it is possible to boost public support for the use of CER as a cost-control strategy. We investigate one potential source of public support: Americans' trust in physicians as faithful agents of patient interests. We conducted two national surveys to explore the public's confidence in doctors compared to other groups. We find that doctors are viewed as harder workers, more trustworthy, and more caring than other professionals. Through survey experiments, we demonstrate that the support of doctors' groups for proposals to control costs and use CER have a greater influence on aggregate public opinion than do cues from political actors including congressional Democrats, Republicans, and a bipartisan commission. Our survey results suggest that the medical profession's stance will be an important factor in shaping the political viability of efforts to use CER as a tool for health care cost control.