Medicine & USMLE


Diabetes Drugs
  1. Insulin Overview
  2. Rapid Acting Insulin
  3. Short Acting Insulin
  4. Intermediate Acting Insulin
  5. Long Acting Insulin
  6. Metformin
  7. Sulfonylureas
  8. Meglitinides
  9. Thiazolidinediones (TZDs)
  10. DPP-4 Inhibitors
  11. Incretin Mimetics
  12. SGLT2 Inhibitors
  13. Alpha Glucosidase Inhibitors
  14. Pramlintide


Metformin is a drug that belongs in the drug class biguanides and is used to treat type 2 diabetes mellitus. It does this by decreasing glucose production in the liver and increasing insulin sensitivity. Side effects of metformin include nausea and vomiting, as well as other GI effects. Metformin should be used with caution in patients with kidney damage and stopped 48 hours before a procedure that uses IV contrast dye. Lactic acidosis is a dangerous side effect of metformin, and patients should drink alcohol with caution to lower the risk of developing lactic acidosis. Metformin does not cause hypoglycemia like several other diabetes medications and for this reason it is one of the safest diabetes drugs available. Finally, metformin can cause weight loss.

Key Points

  • Metformin
    • Drug Class
      • Biguanide
    • Mechanism
      • Decreases liver glucose production
        • Metformin slows the process by which glucose is produced in the liver, called gluconeogenesis
      • Increases insulin sensitivity
    • Clinical Use
      • Treats Diabetes Mellitus Type 2
        • Metformin lowers blood glucose levels
    • Side Effects
      • Lactic acidosis
        • A buildup of lactic acid in the blood
        • A serious medical condition that can be fatal
        • Instruct the patient to report the following symptoms to their provider: muscle pain (myalgia), drowsiness, hyperventilation
        • Use alcohol with caution
          • Alcohol increases the lactic acid buildup, putting the patient at a higher risk for lactic acidosis
      • Nausea/Vomiting
        • Metformin can also cause other GI side effects like loss of appetite (anorexia), diarrhea, and heartburn
        • Most common side effect of metformin
      • Weight loss
        • May be due in part to the GI side effects
      • Use with caution in kidney damage
        • Metformin is excreted by the kidneys
        • Functioning kidneys are required to eliminate the drug from the body. Patients with kidney damage may receive an altered dose of metformin.
      • Do not take metformin within 48 hours of a procedure with IV contrast dye
        • Procedures include cardiac cath, MRI with contrast, CT with contrast
        • IV contrast dye causes temporary kidney damage, which prevents metformin from being excreted and causes the drug to build up in the body. This puts the patient at higher risk of experiencing side effects.
        • Metformin can be resumed once kidney function levels are within normal limits
      • Does not cause hypoglycemia
        • Because metformin doesn’t stimulate a release of more insulin, it has a low risk of causing hypoglycemia
        • This is unique to metformin, most other diabetes drugs do have a risk of hypoglycemia