The Role of Antidiabetic Therapies in Mild Cognitive Impairment and Alzheimer's Disease: A Systematic Review of Metformin, Pioglitazone, and GLP-1 Receptor Agonists.

Alzheimer's disease (AD) and mild cognitive impairment (MCI) are major causes of cognitive decline. Antidiabetic medications such as metformin, pioglitazone, and GLP-1 receptor agonists have been proposed as potential neuroprotective therapies. We assessed whether these agents slow cognitive decline or disease progression in people with AD or MCI. PubMed, Embase, and Cochrane Central were searched for randomized controlled trials and observational studies of metformin, pioglitazone, or GLP-1 receptor agonists in AD/MCI. Results were synthesized narratively by drug class. Eleven studies met the inclusion criteria. Metformin, particularly in early-stage disease and metabolically vulnerable groups, demonstrated improvements in episodic memory and selective executive outcomes. Observational data in diabetic MCI suggested improved cognition and preservation of hippocampal and cortical structure, with limited amyloid-β and tau changes. Pioglitazone findings varied. Benefits were mainly reported in mild AD with type-2 diabetes, but not in non-diabetic AD/MCI. GLP-1 receptor agonists demonstrated preserved cerebral glucose metabolism and improved blood-to-brain glucose transport but did not improve cognitive function. Current evidence does not support antidiabetic therapies as effective treatments in AD/MCI. Any benefits appear to depend on disease stage and metabolic status, with metformin being the most promising candidate. Larger, longer-duration biomarker-defined trials are needed to determine whether any sustained clinical benefit is observed.