Does metformin cause diarrhea? What to do?

Endocrinologist Advise on Metformin Induced Diarrhea

If you started taking metformin you probably have some questions now.  Such as, does metformin cause diarrhea?  What other side effects does metformin have other than diarrhea?  The short answer is most of the time yes.  The real question is how to avoid diarrhea and what to expect when to take metformin.  In the last 15 years, metformin has become the first-line agent for the treatment of type 2 diabetes. Metformin studies showed good safety data.  Diarrhea, however, remains the same as the biggest side effect. Up to 25% of patients suffer metformin-associated gastrointestinal side effects. Approximately 5-10 % of diabetic patients can not tolerate metformin at all. So, should you stay on it? Read the entire article and you will be well versed about metformin side effects.

We also need to mention that a lot of people do not have any side effects from metformin at all.  Metformin sometimes works great.  In other cases, patients have no efficacy from the medication but they get a lot of side effects.  Some people think that response to metformin could be somewhat heritable.

Why does metformin cause diarrhea?

Metformin increases glucose absorption in the intestines.  That can lead to lactic acid formation which can irritate the intestinal system.  Metformin also increases a hormone called incretin.  Incretins can also induce diarrhea. You may remember from previous trulicity or ozempic articles that incretins do a lot.

Metformin can also increase the bile acid in the intestinal system which can change stool consistency.

Metformin can change the bacterial flora in the intestinal system.  This normally helps improve diabetes but also can lead to diarrhea due to changes in the intestinal flora.

Finally, metformin has structural similarities to serotonin receptors.  Serotonin release can cause nausea vomiting and diarrhea as well.

If you have tried and can’t tolerate metformin consider using SugarMD Super Berberine which is a great product that can potentially replace metformin. Read more about it here. 

How to avoid or reduce the risk of diarrhea metformin causes?

  • Start with a very low dose of metformin.
  • Try to use the extended-release form of metformin instead of regular metformin. Modified-release formulations of metformin can spread the absorption of metformin along the gut.  Therefore, it reduces local concentrations of the drug, with the aim of increasing its tolerability.
  • Start taking not more than 500 mg a day.
  • Start taking metformin always with meals.
  • The evening meal is the best time to start taking metformin.
  • If you are taking instant release tablets, swallow whole.  Do not try to chew, crush or break the tablet.
  • If you have a swallowing problem talk to your diabetes doctor.  Suspension for metformin is also available.  For the suspension, you will need to shake well before the use.
  • Only titrate the metformin dose up after side effects subside
  • You can increase the metformin to 500 mg twice a day with meals only if metformin 500 mg is tolerated with the evening meal.
  • If twice a day is tolerated with 500 mg tablets, you can increase it to 2 tablets twice a day for maximum efficacy.
  • More than 2000 mg of metformin is not going to be any more effective than 2000 mg of metformin.
  • Sometimes giving a break to taking metformin for a few weeks may help reduce diarrhea.  Restarting metformin may not give diarrhea again after his break.
  • If diarrhea happens or you are throwing up, call your doctor. You will need to drink more fluids to keep from losing too much fluid.
  • If you are 65 or older, use this drug with care. You could have more side effects.

What other side effects does metformin cause?

Not only diarrhea but also nausea or vomiting can happen.  Excessive gas is not uncommon.  Some people describe chest discomfort.  This chest discomfort is not typically related to heart problems unless there is underlying heart disease.  Metformin can also cause flushing and palpitations.

5 to 6% of people report headaches.  Up to 10% of people can report changes in the tasting of food.  1 to 10% of patients may have excessive sweating, abdominal pain, or indigestion.

B12 levels can go down.  Metformin can very rarely cause low blood sugars.

Lactic acidosis can be concerning for many patients.  On the other hand, the incidence of lactic acidosis with metformin is extremely rare.  Unless a contraindication exists to the use of metformin lactic acidosis should not be a fear factor.  In any case please call your diabetes specialist if you have signs of too much lactic acid in the blood (lactic acidosis) like fast breathing, fast or slow heartbeat, a heartbeat that does not feel normal, very bad upset stomach or throwing up, feeling very sleepy, shortness of breath, feeling very tired or weak, very bad dizziness, feeling cold, or muscle pain or cramps.

Contraindications to metformin

Do not take metformin if you have the following.

  • Impaired renal function with chronic kidney disease stage IV. Early-stage kidney disease is not a contraindication to metformin.  Metformin also does not increase the risk of kidney failure. When you are on metformin, diarrhea can lead to dehydration.  Dehydration can trigger kidney function worsening.
  • Active or progressive liver disease
  • Active alcohol abuse
  • Unstable or acute heart failure. When you end up in the hospital due to heart failure this is typically an acute heart failure.
  • Past history of lactic acidosis during metformin therapy
  • Decreased tissue perfusion or hemodynamic instability due to infection or other causes

What happens if you miss a metformin dose?

Skipped the missed dose and go to your normal routine the next day.

Do not take 2 doses at the same time or double the doses.

How to store metformin?

Store it at room temperature in a dry place.  Do not keep metformin in the bathroom.

Keep metformin away from children and pets.

Pay attention to metformin’s expiration date.  Typically patients will have piles of metformin sitting in their home.  Patients will stop taking metformin due to side effects.  At a later date, the physician may restart.  Patients will resume their previous metformin prescription that may be already expired.

Metformin may not be the best drug for you.  At we will make sure that you get the best medication you deserve. SugarMD Advanced Glucose Support, Super Berberine, and Neuropathy support may be all you need to help regulate your blood sugars and prevent diabetic complications. If you want to learn more about this topic check out our metformin review article.


About the author: Dr. Ahmet Ergin is the author of The Ultimate Diabetes Book and the Founder of the SugarMD youtube channel. He practices in Port Saint Lucie, FL as an endocrinologist physician.


Leave a Reply

Your email address will not be published.