BACKGROUND: Non-steroidal anti-inflammatory drugs (NSAIDs) may exacerbate COVID-19 and worsen associated outcomes by upregulating the enzyme that SARS-CoV-2 binds to enter cells. To our knowledge, no study has examined the association between NSAID use and the risk of COVID-19-related outcomes. METHODS: We conducted a cohort study using South Korea's nationwide healthcare database, which contains data of all subjects who received a test for COVID-19 (n=69,793) as of April 8, 2020. We identified adults hospitalized with COVID-19, where cohort entry was the date of hospitalization. NSAIDs users were those prescribed NSAIDs in the 7 days before and including cohort entry and non-users were those not prescribed NSAIDs during this period. Our primary outcome was a composite of in-hospital death, intensive care unit admission, mechanical ventilation use, and sepsis; our secondary outcomes were cardiovascular complications and acute renal failure. We conducted logistic regression analysis to estimate odds ratio (OR) with 95% confidence intervals (CI) using inverse probability of treatment weighting to minimize confounding. RESULTS: Of 1,824 adults hospitalized with COVID-19 (mean age 49.0 years; female 59%), 354 were NSAIDs users and 1,470 were non-users. Compared with non-use, NSAIDs use was associated with increased risks of the primary composite outcome (OR 1.54 [95% CI 1.13-2.11]) but insignificantly associated with cardiovascular complications (1.54 [0.96-2.48]) or acute renal failure (1.45 [0.49-4.14]). CONCLUSION: While awaiting the results of confirmatory studies, we suggest NSAIDs be used with caution among patients with COVID-19 as the harms associated with their use may outweigh their benefits in this population.