OPED is a database that was established in 1990 to capture Danish patients’ reimbursement of medicines, based on reports from community pharmacies to the Danish Health and Medicines Authority. Since 2007, it covers the whole region of Southern Denmark (population 1,200,000), and since 2009-2012, also covers Region Zealand. With these extensions, the population in this database is approximately two million people. All pharmacies in the included areas have contributed data to OPED and data also cover residents at nursing homes. OPED's data include the Danish Civil Registration Number (CPR), which enables unambiguous linkage with virtually all other health-related registers in Denmark and supports research.