Effects of Liraglutid, Dapagliflozin and Acarbose on the Cognitive Function, Olfactory Function, and Odor-induced Brain Activation in Overweight/Obese T2DM Patients Controlled Inadequately With Metformin Monotherapy.

Inclusion Criteria: * Age ≧ 40 and ≦75 years old * T2DM patients controlled with metformin monotherapy with stable, maximum tolerated doses (≧1500mg/d, ≧12 weeks) * HbA1c\>7% and ≤9% * Body mass index(BMI) ≥25kg/m2 and with stable weight during previous 3 months * Right handedness * Possessed over 6-year education * Provision of informed consent prior to any study specific procedures * Mini-Mental State Examination (MMSE) \>24 Exclusion Criteria: * Allergies to research drugs * Treated with glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, sodium-glucose cotransporter 2 inhibitors, insulins, and glycosidase inhibitors in the previous 6 months * Moderate to severe renal dysfunction defined as estimated glomerular filtration rate(eGFR)\<60ml/min/1.73m2 ( eGFR was estimated by CKD-EPI creatinine equation using an online calculator). * Hepatic insufficiency * A history of neurological and psychiatric disorders, nasal pathologies, abnormal thyroid, pancreatitis, repeated urinary tract infection, chronic gastrointestinal dysfunction, any disease that may worsen by intestinal flatulence, alcohol or substance abuse, steroid treatment * Any acute disease * Inability to undergo tests or MRI scanning * Pregnant or lactating women * Participating in other clinical trials at the same time or within 6 months prior to the start of the trial