Purpose To study the association between the use of drugs for hypertension or heart failure, particularly diuretics, and risk of death in COVID-19.Methods We conducted a cohort study, based on record linked individual-based data from national registers, of all Swedish inhabitants 50 years and older (n = 3,909,321) at the start of the first SARS-CoV-2 wave in Sweden. The association between use of angiotensin-converting enzyme inhibitors (ACEI), angiotensin II receptor blockers (ARB), thiazides, loop diuretics, aldosterone antagonists, beta blocking agents and calcium channel blockers at the index date 6 March 2020, and death in COVID-19 during 7 March to 31 July 2020, was analysed using Cox-proportional hazards regression, adjusted for a wide range of possible confounders.Results Use of loop diuretics was associated with higher risk [adjusted hazard ratio (HR) 1.26; 95% confidence interval (95% CI) 1.17-1.35] and thiazides with reduced risk (0.78; 0.69-0.88) of death in COVID-19. In addition, lower risk was observed for ACEI and higher risk for beta-blocking agents, although both associations were weak. For ARB, aldosterone antagonists and calcium channel blockers no significant associations were found.Conclusion In this nationwide cohort of nearly 4 million persons 50 years and older, the use of loop diuretics was associated with increased risk of death in COVID-19 during the first SARS-CoV-2 wave in Sweden. This contrasted to the decreased risk observed for thiazides. As treatment with loop diuretics is common, particularly in the elderly, the group most affected by severe COVID-19, this finding merit further investigation.