Metformin in T2DM: neurocognitive mechanisms and precision pharmacotherapy.

Type 2 diabetes mellitus (T2DM) is a complex metabolic disorder that significantly predisposes individuals to delirium and dementia through multifaceted neurobiological pathways. The essence of this neurocognitive decline involves mechanisms such as central insulin resistance, chronic low-grade inflammation, and mitochondrial dysfunction. While metformin remains the cornerstone of T2DM management, its impact on the central nervous system exhibits a "double-edged sword" nature, balancing intrinsic neuroprotective properties against the potential neurotoxicity associated with vitamin B12 deficiency. This review aims to systematically synthesize epidemiological and clinical evidence linking metformin to neurocognitive outcomes, contrasting its efficacy with newer glucose-lowering agents such as GLP-1 receptor agonists and SGLT2 inhibitors. In addition, it sheds light on the reciprocal connectivity between systemic metabolic regulation and direct CNS modulation, specifically elucidating AMPK activation, the autophagy-lysosome axis, and the gut-brain and liver-brain axes. We review these molecular mechanisms to delineate the delicate trade-off between neuroprotection and risk, providing a framework for precision pharmacotherapy and biomarker-guided stratification in high-risk T2DM populations.