BackgroundGastrointestinal adverse events (GI AEs) are the main dose-limiting side effects of metformin in type 2 diabetes mellitus (T2DM), reducing adherence and compromising long-term glycaemic control. Current strategies (dose adjustment or combination therapy) seldom address both tolerability and sustained metabolic efficacy. Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation technique that may modulate gut–brain–metabolic pathways—vagal reflexes, infl