Metformin, a member of the biguanide class of antihyperglycemic agents, has been a cornerstone in the management of type 2 diabetes mellitus since its introduction in the mid-twentieth century. In addition to its well-established role in glycemic control, metformin exerts several extra-glycemic actions that significantly broaden its therapeutic potential. These include weight loss, anti-inflammatory effects, modulation of the gut microbiota, and possible anticancer properties. This multifaceted pharmacological profile highlights metformin’s relevance not only in the treatment of hyperglycemia but also within a broader framework of metabolic health and disease prevention. Looking forward, future strategies aimed at optimizing metformin’s benefits may include the development of combination therapies that potentiate its efficacy when used alongside other pharmacological agents or lifestyle interventions. Moreover, personalized medicine approaches—based on individual genetic, microbiome, and metabolic characteristics—could enable more targeted and effective therapeutic regimens.