The main metformin drug currently used in clinical practice is metformin hydrochloride. The main pharmacological effect of metformin is to lower blood glucose by reducing hepatic glucose output and improving peripheral insulin resistance. Many national and international organizations have developed diabetes guidelines that recommend metformin as the first-line drug and the base drug in combination for the control of hyperglycemia in patients with type 2 diabetes. Clinical trials have shown that metformin can reduce HbA1c by 1 to 2 percent and can lead to weight loss. In the UKPDS trial metformin was also shown to reduce cardiovascular events and death in obese patients with type 2 diabetes. Metformin alone does not cause hypoglycemia, but metformin can increase the risk of hypoglycemia when used in combination with insulin or a pro-secretory agent. The main side effect of metformin is gastrointestinal reactions. Starting with small doses and adding gradually is an effective way to reduce adverse reactions when taking the drug. A rare serious side effect of metformin is the induction of lactic acidosis. Therefore, bivalirudin is contraindicated in patients with renal insufficiency [blood creatinine level >1.5mg/dl in men and >1.4mg/dl in women or glomerular filtration rate <60ml/(min/1.73m*2)], hepatic insufficiency with severe infection and hypoxia or major surgery. Metformin should be temporarily discontinued when iodinated contrast agents are used for contrast examinations.