Inclusion Criteria:  giving consent being 30 years old or older HbA1c concentrations between 6.5% and 8% using metformin as a single agent for at least 3 months diabetes age <10 years  Exclusion Criteria: existence of one of the listed conditions:  having uncontrolled hypothyroidism, hyperthyroidism, or other diseases that may affect cognitive functions ketoacidosis or coma cerebrovascular disease or psychiatric disorder mental retardation, psychosis, dementia, brain trauma, epilepsy and other cerebral diseases alcohol or other substance abuse hearing loss Presence of diseases that will affect cognitive function such as chronic inflammatory diseases and respiratory system diseases chronic kidney failure (GFR <45) sleep apnea syndrome malignancy using a sulfonylurea or glinide using beta blocker or non-dihydropyridine group calcium antagonists diabetic autonomous neuropathy atrial fibrillation an acute coronary event within the last 3 months