Inclusion Criteria:  I. AMI  II. Swedish citizens with a personal ID number ≥18 years and ≤80 years  III. Newly diagnosed prediabetes:  HbA1c 42-47 mmol/mol or Capillary or venous fasting plasma glucose concentration 6.1-6.9 mmol/L or 2-hour post-load capillary glucose concentration 8.9-12.1 mmol/L or 2-h post-load venous plasma glucose concentration 7.8-11.0 mmol/L HbA1c <48 mmol/mol and 2-hour post-load capillary glucose concentration >12.1 mmol/L or 2-h post-load venous plasma glucose concentration >11.0 mmol/L (thus elevated 2-hour glucose levels in the diabetes range but without HbA1c levels diagnostic for diabetes)  IV. Naïve to metformin and other glucose lowering therapy  V. Signed informed consent  Exclusion Criteria:  I. Type 1 diabetes  II. Known type 2 diabetes  III. Indication for glucose lowering treatment  IV. Acute condition with high risk for volume depletion, circulatory shock, hypoxia  V. Serious illness, other than cardiovascular, with short life expectancy  VI. Renal failure (eGFR <60ml/min)  VII. Hepatic failure  VIII. Malignancy within the last year  IX. Contraindication or hypersensitivity to the study drug  X. Alcohol or drug abuse  XI. Pregnancy or breastfeeding  XII. Women of childbearing potential without adequate anticonception during any part of the study period  XIII. Previous hospitalisation for lactic acidosis  XIV. Predicted inability to comply with the study protocol