The use of prescription drugs may influence the risk of developing cancer. In this study, we sought to identify such effects by combining data from Danish nationwide health care registries on drug use and cancer occurrence. We compared drug use among 278,485 cancer patients to use among cancer-free control individuals. Thereby, we identified 1020 putative drug–cancer associations. Future research should address the signals provided by our study, either as studies focusing on single associations or as a replication of our study in other data sources.