Study design and data sources
We conducted a nationwide observational study with annually repeated cross-sectional drug analyses on data from Danish Health Data. We used the Danish National Prescriptions Registry (16), containing data on all pharmacy collected drug prescriptions since 1995; the Danish National Patient Register (17), providing information on all hospital contacts in Denmark since 1977 including International Classification of Diseases (ICD)-10 codes; and the Danish Civil Registration System (18), providing basic personal information on all Danish citizens. Data from the national registers were linked on a personal level via the unique Civil Personal Registration (CPR)-number, assigned to all inhabitants in Denmark at birth or residing longer than three months (18). All CPR-numbers were replaced with pseudomized serial numbers to preserve confidentiality.