Metformin is the first line of oral medication in the treatment of type 2 diabetes as clearly stated in the current guidelines for the prevention and treatment of diabetes, and can lower glucose by reducing insulin resistance and decreasing hepatic glycogen output. However, some populations are contraindicated for metformin. The common ones are: first, patients with severe liver and kidney insufficiency or severe cardiopulmonary disease. For example, patients with heart failure or chronic lung congestion in very poor condition, these are not recommended to take metformin. Second, for example, the complications of diabetes have been more serious, with diabetic nephropathy stage 3 or more or diabetic retinopathy stage 3 or more, is also not recommended to take metformin for a long time. There are also some special circumstances of patients, such as long-term alcoholism, or mental illness patients, is also not suitable for long-term metformin.