The expansion of public health insurance programs affects payers as well as the behavior of service providers. In this paper, we study the expansion of Swiss mandatory health insurance in 2012 to include complementary and alternative medicine physician services. The policy change provides a quasi-experimental design that allows us to estimate the causal effects on the payer and physician behavior using a difference-in-differences framework. First, we find that from the payer's perspective, expanding coverage to complementary and alternative medicine increases physician costs per patient by about 7 percent. Second, we find that the increase in physician service costs per patient in mandatory health insurance is almost exactly offset by a decrease in supplementary health insurance costs. Thus, suggesting that the behavior of physicians was unchanged by the coverage expansion.