Diabetes mellitus, commonly known as diabetes, is a condition characterized by unusually high levels of glucose in the bloodstream. This occurs due to one of two primary reasons: insufficient insulin production by the pancreas, which is responsible for lowering blood sugar, or the cells' reduced sensitivity to insulin's effects. These mechanisms define the two main types of diabetes: insulin-dependent (type 1) and non-insulin-dependent (type 2). In type 1 diabetes, there is either no insulin or not enough of it. In type 2 diabetes, insulin is usually produced in adequate amounts, but the cells do not respond to it effectively.Both types of diabetes share symptoms such as increased urination, decreased appetite, and fatigue. Diagnosis involves blood glucose testing, glucose tolerance tests, and measuring levels of glycated hemoglobin (HbA1c). Treatment strategies vary depending on the specific type of diabetes.Major complications associated with diabetes include dangerously high blood sugar levels, low blood sugar from diabetes medications, and vascular diseases that can affect the eyes, kidneys, nerves, and heart.