Efficacy of Metformin in Preventing Diabetes in China

Main Inclusion Criteria: 1. Diagnosis of IGR before the randomization based on the 1999 WHO diagnostic and classification criteria. 2. Age: 18 ≤age≤70 years old. 3. Not on a treatment of anti-diabetic agents, including Chinese traditional herbs lowering blood glucose for at least 6 months before screening. 4. Male or non-pregnant, non-breastfeeding females, females without birthing plan in next three years. 5. Body mass index (BMI) ：21 kg/m2 ≤BMI\<32 kg/m2. 6. Written informed consent given before any trial-related activities are carried out. Main exclusion Criteria: 1. Administration with medications for pre-existed diseases affect glucose metabolism (except thiazide diuretics when its daily dose≤12.5mg). 2. Administration with anti-obesity agents (including Chinese traditional medicine) within 6 months of enrolment and during intervention. 3. Administration with three or more than three types antihypertensive drugs. 4. Diabetes patients (subjects with prior history of gestational Diabetes will not be excluded). 5. Have any of the following cardiovascular conditions within 3 months prior to the screening visit: acute myocardial infarction, congestive heart failure defined as New York Heart Association class III/IV or left ventricular ejection fraction ≤40%,) or cerebrovascular accident. 6. Persistent uncontrolled hypertension (systolic blood pressure ≥160mmHg, or diastolic blood pressure ≥100 mmHg). 7. Impaired liver function, have obvious clinical signs or symptoms of liver disease, acute or chronic hepatitis, ALT or AST levels ≥3 times the upper limit of the reference range at the screening visit. 8. Renal dysfunction (eGFR\<45ml/min）. 9. Patients ventilated by ventilator. 10. Hypersensitivity to metformin or to any of the excipients such as povidone K 30, magnesium stearate and hypromellose. 11. Disease which may cause tissue hypoxia (especially acute disease, or worsening of chronic respiratory disease). 12. Acute alcohol intoxication, alcoholism. 13. Severe chronic gastrointestinal disease. 14. Severe psychiatric illness. 15. Cancer requiring treatment in past 5 years. 16. Uncontrolled thyroid diseases. 17. Women who are pregnant or breastfeeding . 18. Participation in another clinical trial within the past 30 days . 19. Other significant disease that in the Investigator's opinion would exclude the subject from the trial.