Metformin (Glucophage, Fortamet)
The most widely prescribed oral medication for type 2 diabetes. Decades of data, generally well tolerated, and among the most affordable options available.
What it's used for
First-line treatment for type 2 diabetes, and sometimes prediabetes, PCOS, or weight management adjunct. Lowers blood glucose by reducing liver glucose production and improving insulin sensitivity.
Typical dosing (adults)
- Starting: 500mg once or twice daily with meals.
- Titration: increase gradually to reduce GI side effects.
- Max: 2000-2550mg/day depending on formulation.
- Extended-release (XR): taken once daily; better tolerated for many.
Key interactions & considerations
- Iodinated contrast dye (CT scans): major — usually held 48 hours around the procedure to reduce lactic acidosis risk.
- Alcohol: moderate — increases lactic acidosis risk; causes glucose swings.
- Kidney function: dose must be adjusted or discontinued as eGFR drops.
- Certain diuretics, cimetidine, ranolazine: may raise metformin levels.
Common side effects
GI effects (nausea, diarrhea, metallic taste) — usually settle within 2-4 weeks. Taking with food and titrating slowly helps. Rare: vitamin B12 deficiency with long-term use. Very rare but serious: lactic acidosis.
Who should be cautious
- People with significant kidney or liver disease.
- Heart failure (stable CHF is usually fine; acute decompensation is not).
- Before surgery or contrast imaging — tell your care team you take it.
What to ask your pharmacist
- Should I switch to extended-release for better tolerance?
- Do I need B12 monitoring?
- What should I do on sick days or before a CT scan?