Does Metformin Cause Diarrhea? How to Manage This Gut-Related Side Effect

Metformin lowers blood glucose (sugar) in different ways, and it does its job well. 

This commonly prescribed medication for Type 2 diabetes lowers how much glucose your liver makes, how much glucose is absorbed from food you eat, and it helps your body use its own glucose supply better — all within a few weeks of starting it. What’s more, low blood glucose (hypoglycemia) and weight gain are very rare with metformin. But, these benefits do come with some potential downsides.

Although it's mostly well tolerated, gut-related side effects like diarrhea, nausea and vomiting, and gas can occur. Of these, diarrhea is the most common. Fortunately, diarrhea from metformin is often short-lived. And there are ways you can successfully manage it or prevent it altogether.

Why does metformin cause diarrhea?

The exact reason why metformin can cause diarrhea isn’t fully clear. But we do know that it works in the gut to lower blood glucose. 

So one possible explanation is that metformin can alter the bacteria and viruses that live in your gut (also called the microbiome). This disrupts the normal activity inside your gut. It could possibly lead to more frequent and loose stools as your body tries to readjust. 

Another possible explanation is that metformin alters the movement of certain gut chemicals, like serotonin or histamine. This can lead to diarrhea.

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How common is metformin-related diarrhea?

Diarrhea is common with metformin. You’re not alone if you’ve experienced diarrhea from taking it. In clinical trials, diarrhea occurred in more than half of people who took metformin. 

Unfortunately, some people find this to be an inconvenient and limiting side effect that disrupts their daily routine. The good news is gut-related side effects from metformin tend to improve over time.

How long does diarrhea from metformin last?

For most people, diarrhea is most common during the first few weeks of taking the medication. But these initial weeks can be tough. In one study, about 5% of people reported that gut-related side effects were the reason why they stopped taking metformin. However, know that it tends to get better in later weeks.

If diarrhea from metformin becomes especially bothersome, it’s important to talk to your healthcare provider. They can talk to you about ways to prevent and manage diarrhea, including possible dose adjustments.

Is it possible to prevent metformin diarrhea?

Possibly. The golden rule is to take metformin with a meal or right after a meal. You’re more likely to have gut-related side effects, like nausea and diarrhea, from metformin if you take it on an empty stomach.

It’s a good idea to take it with food from your very first dose and on. Pairing it with a meal, or even storing it in a secure location near your kitchen or dining table, is a good way to build this habit.

If you miss a dose of metformin with your usual meal, take the missed dose as soon as you remember. You may need to eat a snack depending on when your last meal was to avoid taking it on an empty stomach. But if it’s almost time for your next dose, skip the one you missed and take your next dose as normal. No need to double up on doses.

How can you manage diarrhea from metformin?

If you’re taking metformin with food and still experiencing diarrhea, there are some other management tips to try.

Switching formulations from the traditional immediate-release (IR) formulation to the extended-release (ER) formulation is one option. You might also see the ER formulation written as XR — they’re the same thing. Compared to metformin IR, the ER version releases medication more slowly and is less likely to cause gut-related side effects. Making the switch to metformin ER may be one way to tolerate metformin better.

Another way to manage diarrhea from metformin is to work closely with your healthcare provider when starting and adjusting your dosage. For both IR and ER formulations, there is lower risk of having gut-related side effects with slow and careful dosage changes. This is because your body is given more time to adjust to a new dose.

A typical starting dosage for metformin is 500 mg once or twice daily with a meal. If a higher dose is needed, it’s a good idea to raise it by no more than 500 mg every 1 to 2 weeks until you reach your target dose. This gives time for your body to adjust. Raising the dose too quickly or by too much can worsen the risk of diarrhea.

When should I contact my healthcare provider about diarrhea from metformin?

If you’re still having stomach-related side effects after taking metformin for a few weeks, talk to your healthcare provider. They may recommend lowering your dose, switching to the ER formulation, or taking metformin right after a meal. They may also recommend ways to treat medication-induced diarrhea, such as with anti-diarrheal medications, while your body adjusts to metformin.

If none of these changes work, your healthcare provider may suggest stopping metformin altogether and trying a different diabetes medication. But it’s important that you don’t stop taking metformin on your own. Your healthcare provider can walk you through the next steps. 

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Written by:

Hindu Rao, PharmD, APh, BCACP

Hindu Rao, PharmD, APh, BCACP is a clinical assistant professor of pharmacy practice at Chapman University School of Pharmacy and a clinical pharmacist at Providence Medical Foundation. She specializes in chronic disease management and has her board certification in ambulatory care.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Tegan Smedley, PharmD, APh

Tegan Smedley, PharmD, APh, has 10 years of experience as a pharmacist. She has worked in a variety of settings, including retail, hospital, and ambulatory care.

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