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BACKGROUND We hypothesised that the use of the anti-androgenic drug 5α-reductase inhibitors (5-ARIs) improves survival in patients with oesophago-gastric cancer. METHODS This nationwide Swedish population-based cohort study included men who underwent surgery for oesophageal or gastric cancer between 2006-2015, with follow-up until the end of 2020. Multivariable Cox regression estimated hazard ratios (HR) for associations between 5-ARIs use and 5-year all-cause mortality (main outcome) and 5-year disease-specific mortality (secondary outcome). The HR was adjusted for age, comorbidity, education, calendar year, neoadjuvant chemo(radio)therapy, tumour stage, and resection margin status. RESULTS Among 1769 patients with oesophago-gastric cancer, 64 (3.6%) were users of 5-ARIs. Compared to non-users, users of 5-ARIs were not at any decreased risk of 5-year all-cause mortality (adjusted HR 1.13, 95% CI 0.79-1.63) or 5-year disease-specific mortality (adjusted HR 1.10, 95% CI 0.79-1.52). Use of 5-ARIs was not associated with any decreased risk of 5-year all-cause mortality in subgroup analyses stratified by categories of age, comorbidity, tumour stage, or tumour subtype (oesophageal or cardia adenocarcinoma, non-cardia gastric adenocarcinoma, or oesophageal squamous cell carcinoma). CONCLUSION This study did not support the hypothesis of improved survival among users of 5-ARIs after curatively intended treatment for oesophago-gastric cancer.