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Metformin

Brand names: Glucophage, Glumetza, Fortamet

Metformin is usually the first medicine used for type 2 diabetes. It lowers blood sugar by helping your body use insulin better.

Brand namesGlucophage, Glumetza, Fortamet
Type of medicineBiguanide (diabetes medicine)
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

Metformin lowers the amount of sugar the liver releases and helps muscles take in sugar.

On its own it rarely causes low blood sugar, and it doesn't cause weight gain.

What it's used for

  • Type 2 diabetes
  • Sometimes prediabetes or polycystic ovary syndrome (PCOS)

How to take it

  • Take it with meals to reduce stomach upset.
  • Swallow extended-release tablets whole; don't crush or chew them.
  • Your provider usually starts low and raises the dose slowly.
  • You may see the shell of an extended-release tablet in your stool. That's normal.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Diarrhea, gas, or upset stomach (usually improves after a few weeks)
  • Metallic taste
  • Low vitamin B12 with long-term use
Call 911Signs of lactic acidosis: deep, fast breathing, severe weakness, unusual muscle pain, severe stomach pain, feeling very cold, or a slow or irregular heartbeat
Call your provider todayVomiting or diarrhea that keeps you from drinking fluids

Warnings

  • Not used in people with serious kidney problems.
  • You may need to stop it briefly before a CT scan with contrast dye or before surgery.
  • Heavy drinking raises the risk of lactic acidosis.

Other medicines, foods, and alcohol

  • Avoid heavy alcohol use.
  • Some medicines (like topiramate and certain HIV medicines) raise the risk of lactic acidosis.
  • Insulin and sulfonylureas taken with metformin can cause low blood sugar.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Metformin is sometimes used in pregnancy. Talk with your provider about the best plan for your blood sugar.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.