Recombinant insulin, used to treat diabetes, has an enormous impact on diabetes management. However, this essential hormone is prone to aggregation during transportation and storage, reducing its efficacy in glycemic control. To prevent insulin aggregation, here we repurposed an antifungal drug called Nystatin (Nys) identified through a virtual screening of 5500 FDA-approved drugs. Nys effectively inhibited the aggregation of insulin under physiological conditions. Nys-treated insulin was completely soluble, retained its native secondary structure, and was nontoxic to HEK293T cells. Notably, this drug completely abrogated fibrillation of fast-acting insulin formulations Aspart and Lispro, as well as slow-acting insulin, Glargine. The ability of insulin formulations to activate the insulin receptor was maintained after Nys treatment. The efficacy of Nys-treated formulations in maintaining glycemic control was further validated in a diabetic rat model. Thus, this FDA-approved drug has the potential to be used in commercial insulin formulations to maintain stability and activity while preventing its aggregation for an extended period.