Poor information flows hamper coordination, potentially leading to suboptimal decisions in health care. We examine the effects of a large-scale policy of health information integration. We use the staggered adoption of a nationwide electronic prescribing system over four years in Finland and prescription-level administrative data. Our results show no discernible effect on the probability of co-prescribing harmful drugs on average, but the heterogeneity analysis reveals that this probability reduces in rural regions, by 35 percent. This substantial reduction is driven by interacting prescriptions from different physicians and generalists. Information integration can therefore improve the coordination of physicians' interdependent decisions.