Rahmat Sediq,1 Jurjen van der Schans,1 Aafje Dotinga,2 Rolinde A Alingh,2 Bob Wilffert,1,3 Jens HJ Bos,1 Catharina CM Schuiling-Veninga,1 Eelko Hak1,4 1Department of Pharmaco-Therapy, Epidemiology & Economics, University of Groningen, Groningen Research Institute of Pharmacy, Groningen, the Netherlands; 2Lifelines Cohort Study, Lifelines Databeheer B.V., Groningen, the Netherlands; 3Department of Clinical Pharmacy and Pharmacology, University Medical Center Groningen, Groningen, the Netherlands; 4Department of Epidemiology, University Medical Center Groningen, Groningen, the Netherlands Background: While self-reported data are commonly used as a source of medication use for pharmaco-epidemiological studies, such information is prone to forms of bias. Several previous studies showed that various factors like age, type of drug and data collection method may influence accuracy. We aimed to assess the concordance of the self-reported medication use that was documented at entry to the Lifelines Cohort Study, a three-generation follow-up study in the Netherlands that started in 2006 and included over 167,000 participants. Materials and methods: As part of the PharmLines Initiative, we collected medication data from the Lifelines participants encoded according to the Anatomical Therapeutic Chemical (ATC) coding scheme and linked the data via Statistics Netherlands to the widely used and representative pharmacy prescription database of the University of Groningen, IADB.nl. Analyses were conducted at second level of ATC coding for all recorded medications as well as a top list of most used medications at drug-specific fifth level. Cohen’s kappa statistics were used to measure the concordance for all participants according to sex and age. Results: The level of concordance between the two data sources largely differed according to the therapeutic class. Medication used for the cardiovascular system and diabetes, thyroid therapy, bisphosphonates and anti-thrombotic drugs showed a very good agreement (κ>0.75). ...