Why does metformin cause stomach upset?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Metformin commonly causes stomach upset, including diarrhea, nausea, gas, bloating, and abdominal discomfort. These gastrointestinal side effects occur because metformin alters gut motility, increases intestinal glucose use, and changes the gut microbiome. Symptoms are most common when starting the medication or increasing the dose, and often improve within a few weeks. Taking metformin with food or switching to an extended-release form can help reduce these effects.

If you're experiencing ongoing stomach issues, it's important to determine whether metformin is the true cause—or if something else is going on. A free, instant, online symptom check can help you identify possible causes based on your specific symptoms and guide your next steps, whether that's adjusting your routine or talking to your doctor. Understanding what's driving your discomfort is the first step toward feeling better.

Reviewed for medical accuracy: 07/20/2026

Important Next Steps

Discover why metformin upsets your stomach Learn if metformin side effects need care See if symptoms suggest a metformin issue Find OTC relief for metformin stomach upset Find a doctor for metformin side effects Discover medically valid remedies for stomach upset Understand if metformin symptoms need urgent care

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Explanation

Metformin is a common medicine used to help control blood sugar levels in people with diabetes. However, it can cause stomach problems for some people.

How It Affects the Stomach

Intestinal Effects: Metformin can change how your intestines absorb sugar, which might lead to diarrhea and stomach upset.
Gut Flora: It may also affect the bacteria in your gut, leading to symptoms like gas and bloating.

Managing Stomach Upset

Extended-Release Option: Some people find that taking an extended-release form of metformin helps reduce stomach issues because it releases the medicine slowly over time.
Starting Slowly: Doctors might start you on a low dose and gradually increase it to help your body get used to the medicine.

If you experience stomach upset while taking metformin, it's important to talk with your healthcare provider. You can also use our free symptom checker to better understand your symptoms before your appointment. They can help you find ways to manage these side effects, like adjusting your dose or switching to a different form of the medicine.

(References)

Bonnet F, & Scheen A. (2017). Understanding and overcoming metformin gastrointestinal .... Diabetes, obesity & metabolism, 27987248.
Foss MT, & Clement KD. (2001). Metformin as a cause of late-onset chronic diarrhea. Pharmacotherapy, 11714216.
Jabbour S, & Ziring B. (2011). Advantages of extended-release metformin in patients with .... Postgraduate medicine, 21293080.

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