ObjectivesThe primary aim of this study was to evaluate whether a high Medication Risk Score (MERIS) upon admission to an emergency department is associated with increased risk of 30-day readmission in patients discharged directly home. Mortality, visit to general practitioner, and drug changes within 30 days were included as secondary outcomes.MethodsThis is a historical cohort study with data from the Danish population-based open-cohort CROSS-TRACKS. Cox regression analyses were used to determine whether a high MERIS score was associated with increased risk of 30-day readmission and mortality. Visit to general practitioner and drug changes were tested with χ2 test and Wilcoxon rank sum test.ResultsA total of 2106 patients were eligible: 2017 had a MERIS score lower than 14 (low-risk group), and 89 had a score of 14 or higher (high-risk group). The proportion of patients in the high-risk group who were readmitted was 21.3% compared with 16.3% in the low-risk group, resulting in a hazard ratio for readmission of 1.43 (95% confidence interval, 0.9–1.3). The hazard ratio for mortality was 8.3 (95% confidence interval, 3.0–22.8). No statistical significant difference was found in general practitioner visits; however, significantly more drug changes were observed in the high-risk group.ConclusionsA high MERIS score was associated with increased risk of readmissions and can potentially assist healthcare professionals in the prioritizing of patients who may benefit from further exam, for example, additional medication review in acute care setting. Further investigation of MERIS and exploration of causal inferences between medication-related harm and medication-related readmissions are warranted.