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.