Side effects of metformin (( full information ))

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Common Side Effects of Metformin

Stomach upset is the most common side effect of metformin. About 25% of people have problems such as:

  • swelling
  • gas
  • Diarrhea
  • Abdominal pain
  • Constipation
  • low appetite

Taking metformin with food may help. If you increase your dose, these side effects may return.

While doctors used to avoid prescribing this drug to people who have kidney problems, it may be okay for someone with mild or moderate kidney disease.

You may see the shell part of the extended-release tablet in your stool. If you do, don’t worry. The medicine has gone into your body, and you should not take any extra pills.

A large study has linked long-term use of metformin to a higher chance of developing Alzheimer’s disease and Parkinson’s disease. But more research is needed to better understand the connection and what it means.

Rare side effects of metformin

Some people (in one study, it was less than 5%) reported heartburn, headache, upper respiratory infections, and a bad taste in their mouth when taking extended-release metformin. Those side effects were had by 12% of people on the regular formula. They also reported flu-like symptoms, sweating, flushing, heartburn, rashes and nail problems.

Serious Side Effects of Metformin

lactic acidosis

This is a dangerous condition caused by a buildup of lactic acid, a chemical that your muscles and red blood cells make naturally. When this happens while taking metformin, it is called metformin-associated lactic acidosis (MALA).

The problem is very rare, occurring in a small fraction of people taking the drug.

This is more likely to happen if you:

  • have kidney or liver disease
  • drink a lot
  • have severe congestive heart failure
  • are sick with fever, diarrhea, or vomiting
  • are dehydrated

Many of the warning signs are similar to some metformin side effects, such as abdominal pain, dizziness, and weakness. Others have numbness or chills in your limbs, or a change in your heart rate. If you notice any of these problems, contact your doctor immediately.

Vitamin B12 deficiency

Anyone can be deficient in this B vitamin, but the risk is higher on metformin, especially over time. When you don’t get enough, it can lead to peripheral neuropathy, numbness or tingling in your feet and legs that already puts you at risk for diabetes. It can also cause anemia, a low level of red blood cells.

Ask your doctor to check your B12 level regularly. Don’t wait until you have symptoms. It is also a good idea to include naturally high B12 foods in your diet. Beef liver and clams contain the most. Chicken, beef, eggs, dairy products and fortified cereals are good sources. Supplements can also bring your levels back to normal, especially if you are a vegetarian. Just talk to your doctor before you start taking one.


If you take metformin while fasting or doing very heavy physical activity your blood sugar may drop too low.

If you are taking metformin with a combination pill, or other diabetes medicines or insulin, check with your doctor how likely you are to have low blood sugar. If you are taking metformin yourself, you probably will not have low blood sugar.

Who is at higher risk of serious side effects?

Because of the risk of serious problems, your doctor will probably recommend a different medicine if you:

  • Have had an allergic reaction to metformin or other drugs
  • Have diabetes that is not under control
  • Have liver or kidney problems
  • Have a serious infection
  • Recently had a heart attack or heart failure
  • Have breathing or blood flow problems
  • Drink a lot

Management of Metformin Side Effects

Some side effects go away on their own with time. There are a few ways to reduce or avoid problems:

  • Ask to start on a low dose. This makes it easier for your body to adjust to the medicine.
  • Take metformin with food. It is okay to take the medicine on an empty stomach, but taking it with food makes it easier to handle.
  • Ask about the extended-release form of metformin. You’ll take it once a day instead of twice. Since it does not release the drug all at once, the side effects are often mild. In one study, only 10% of people taking the extended-release form had diarrhea, while 53% of those taking the standard formula had diarrhea. Just 7% had nausea, compared to 26%. And less than 1% of people on extended-release metformin had to stop taking it because of side effects.

Metformin Drug Interactions

Metformin can cause problems with other medicines you take, including diuretics, glaucoma medicines, corticosteroids, thyroid medicines, birth control pills, and other estrogen medicines, and calcium channel blockers. Also, if you take metformin with medicines for acid reflux, you may be more likely to have a vitamin B12 deficiency. Be sure to note everything you take with your doctor.

Before you can have an imaging test that uses a contrast dye, such as a CT scan or MRI, you must stop taking metformin. The combination of dye and medication can cause a reaction that leads to lactic acidosis. Tell your health care team that you take metformin before having an imaging test.

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