More than 30 states have enacted laws mandating use of prescription drug monitoring programs (PDMP) to reduce inappropriate opioid prescribing. Clinicians in those states must check the PDMP database before writing opioid prescriptions. These mandates vary substantially across states in their timing and scope; for example, some exempt patients with cancer.1,2 We examine the association between state mandatory-access PDMPs and changes in the percent of oncologists’ Medicare patients with any opioid prescription fills.