AbstractBackgroundAndrogen deprivation therapy (ADT), used increasingly in the treatment of prostate cancer (PCa), negatively influences glycemic control in diabetes and is associated with an increased risk of diabetes complications where hospitalization commonly ensues. Metformin could decrease the metabolic consequences of ADT and enhance its effect. This study examined the association of metformin use with healthcare resources utilization among diabetic, PCa patients receiving ADT.MethodsDiabetic adults with PCa on ADT in Hong Kong between December 1999 and March 2021 were identified. Patients with <6 months of concurrent metformin and ADT use were excluded. All included patients were followed up until September 2021. The outcomes were hospital attendances and related costs.ResultsIn total, 1,284 metformin users and 687 non‐users were studied. Over 8,045 person‐years, 9,049 accident and emergency (A&E), and 21,262 inpatient attendances, with 11,2781 days of hospitalization were observed. Metformin users had significantly fewer A&E attendances (incidence rate ratio (IRR): 0.61 [95% confidence interval 0.54–0.69],p< 0.001), inpatient attendances (IRR: 0.57 [0.48–0.67],p< 0.001), and days of hospitalization (IRR: 0.55 [0.42–0.72],p< 0.001). Annual attendance costs were lower for metformin users than non‐users (cost ratio: 0.28 [0.10–0.80],p= 0.017).ConclusionsMetformin use was associated with decreased hospital attendances, days of hospitalization, and associated costs, which could help reduce healthcare resource utilization following ADT in the treatment of PCa.