Why does metformin cause diarrhea?

Metformin is an oral medication used along with diet and exercise to treat people with type 2 diabetes. According to the manufacturer, about 53% of people taking metformin immediate-release tablets experienced diarrhea in one clinical study. In another study, 10% of people taking metformin extended-release tablets reported diarrhea as a side effect.

Why does metformin give you diarrhea?

Diarrhea can happen when your dose of metformin is raised too quickly, or if you take too high of a dose. It’s not fully clear why metformin causes diarrhea as a side effect. Researchers believe it could be due to the following reasons:

• A change in gut microbiome
• Increased bile acid concentration in the intestines
• Increase in glucagon-like peptide 1 (GLP-1) concentration
• Higher amount of serotonin activity in the intestines
• Disruption of histamine breakdown in the intestines
• Increased intestinal glucose

The diarrhea caused by metformin could be partly due to an osmotic effect, since it seems to cause a higher amount of bile acids and glucose in the intestines. This could draw more water into the intestines, leading to diarrhea.

Metformin might also increase certain substances in the intestines, like GLP-1, serotonin, and histamine, that are linked with gastrointestinal symptoms like diarrhea. Studies have also shown that metformin can change the bacteria that live in our intestines, which might cause diarrhea too.

For most people, diarrhea from metformin is most common right after starting it. However, it can sometimes begin after the first few weeks of taking it, or even at any time during treatment.

Related questions

• How long does metformin take to work?
• When is the best time to take metformin?
• What is the safest diabetes medication?

How long does diarrhea caused by metformin last?

The amount of time it takes for diarrhea caused by metformin to go away is different for everyone. It generally goes away after a while, as your body gets used to the medication. If it lasts more than a few weeks, make sure to tell your doctor. Also let your doctor know if the diarrhea goes away and then comes back again.

How do I stop metformin from giving me diarrhea?

One thing you could do to help prevent diarrhea from metformin is to take your doses with meals. If that’s not helping, talk to your doctor to see if you could try a lower dose or change to a different formulation or medication. The extended-release (ER) version of metformin appears to cause less diarrhea as a side effect compared to the immediate-release (IR) version. Don’t stop taking metformin without first consulting your doctor.