Metformin beyond Glycemic Control: New Mechanistic Insights and Expanding Therapeutic Horizons

Metformin, while central to diabetes management, functions as a highly pleiotropic agent with mechanisms that extend far beyond simple glycemic control. In age-related degenerative diseases, including neurodegenerative disorders, it may modulate mitochondrial function, reduce oxidative stress, and influence longevity-related pathways, suggesting possible anti-aging effects. Emerging evidence also points to anticancer activity, with studies reporting reduced incidence and improved outcomes across several malignancies, potentially through mammalian target of rapamycin (mTOR) inhibition, metabolic reprogramming, and suppression of inflammatory signaling. Furthermore, the ‘intestinal glucotonic effect’ has been proposed to involve glucose excretion from the circulation into the gut lumen through reactive oxygen species-dependent upregulation and membrane localization of glucose transporter type 1 (GLUT1), an adenosine monophosphate-activated protein kinase (AMPK)-independent process that may contribute to the reprogramming of systemic glucose flux and provides metabolic substrates for the microbiota. Metformin also alters the gut microbiome by increasing the abundance of multiple short-chain fatty acid-producing bacteria and enhancing intestinal barrier function, which may contribute to systemic metabolic and immunologic benefits. Collectively, metformin is a pleiotropic agent with broad effects on aging biology, cancer pathophysiology, host–microbiome interactions, and immunometabolic regulation. Despite decades of clinical use, important gaps remain in understanding how these mechanisms converge to influence outcomes in individuals with diabetes and beyond.