Can Metformin Cause Diarrhea or Chronic Diarrhea?

Key takeaways:

• Metformin is a medication commonly used to treat type 2 and gestational diabetes.
• Diarrhea, nausea, and stomach pain are some of the most common side effects of metformin.
• The development of gastrointestinal side effects can occur even after years of metformin use.

Metformin is a common medication prescribed as one of the first-line treatment options for patients with type 2 diabetes. Alongside lifestyle changes like regular exercise and a balanced diet, metformin helps many patients successfully manage symptoms and stay healthy. Although it effectively reduces blood sugar levels, metformin can cause side effects, including diarrhea, nausea, and stomach pain.

Dealing with these effects can be frustrating, especially because they may make it more difficult to continue with your treatment as prescribed. Identifying whether your diarrhea symptoms are related to metformin can help you determine whether it’s the right treatment option for you.

Is it normal to have diarrhea or chronic diarrhea when taking metformin?

Metformin is the initial medication choice for most patients with type 2 diabetes. The medication reduces blood glucose levels and helps patients avoid side effects like weight gain and hypoglycemia, which are common side effects of other diabetes medications.

Diarrhea is a common side effect of metformin, so experiencing diarrhea while taking the medication can be normal. The good news is that this diarrhea usually resolves over time.

With long-term use of metformin, cases of chronic diarrhea are rare. It is a generally well-tolerated medication that’s safe for long-term use. Still, before starting metformin, your physician may suggest lifestyle modifications, like dietary changes and increased exercise, to help lower your hemoglobin A1C without medication.

How metformin causes diarrhea

The exact mechanism of how metformin causes diarrhea is not well-known despite how common the side effects are. Estimates suggest that 5 to 8% of patients have had to stop taking metformin due to gastrointestinal side effects.

Some experts theorize that metformin causes diarrhea through changes in how certain substances (like a transporter called OCT1) are moved through the body. Other changes metformin causes that could lead to diarrhea include faster digestion, an increase in GLP-1 production, or issues with how bile (a digestive fluid) gets processed.

However common they may be, metformin side effects like nausea, gas, vomiting, abdominal pain, and diarrhea are often reversible. They are most likely to occur when first starting metformin, but some patients can experience diarrhea even after using the medication for some time. Some risk factors include:

• Rapid dosage increase
• Using immediate-release metformin
• A history of chronic gastritis
• Bacterial infections of the stomach, such as Helicobacter pylori
• Taking medications such as verapamil or proton pump inhibitors

How to tell the difference between metformin diarrhea and other types of diarrhea

It is sometimes unclear whether your diarrhea is due to metformin usage or other causes of diarrhea.

You may be able to determine the culprit by considering the timing and length of your symptoms. Additionally, consider any factors that seem to make your symptoms better or worse.

Other common causes of diarrhea

Your diarrhea may not be due to metformin, and it’s important to be aware of some other common causes. Before diving into deeper detail about these causes, let’s first define what classifies as diarrhea.

Diarrhea is an increase in the number of daily bowel movements, generally more than three movements daily, and loose stool consistency. If your stool appears looser than normal and is similar to types 5 and 7 on the Bristol stool chart, you may be experiencing diarrhea. There are numerous causes of diarrhea other than metformin, discussed in further detail below.

Gastroenteritis

The most common cause of diarrhea is gastroenteritis (stomach flu). This is an inflammation of the gastrointestinal tract, usually due to a viral or bacterial infection. Although less common, parasites can also cause gastroenteritis. Other symptoms include stomach pain, nausea, and vomiting.

You may be at an increased risk of developing gastroenteritis if you have been around someone with similar symptoms, been exposed to contaminated food or water, recently had a cold, or have any condition that affects your immune system.

Food poisoning, antibiotics, and other medications

Metformin is not the only medication that can lead to diarrhea. Eating contaminated foods or liquids can increase your risk of developing gastroenteritis or affecting your gastrointestinal tract in a way that would lead to diarrhea. Antibiotics are a common type of medication that can lead to gastric side effects.

If you recently started taking or have completed a course of antibiotics for an infection, this may be the cause of your diarrhea. Similarly, many other medications can also cause diarrhea, so speak with your primary care provider to see if any of the medications you are currently or have recently taken may cause diarrhea as a side effect.

Malabsorptive syndromes and food sensitivities

Certain groups of foods may be causing your diarrhea. If you notice that your symptoms are particularly worse after eating a specific food or group of foods, your symptoms may be due to a malabsorptive syndrome or a food sensitivity.

Many foods can cause diarrhea. Some examples include artificial sweeteners, dairy if you’re lactose intolerant, and gluten if you have Celiac disease. You may also react to other foods that you are developing a sensitivity to.

If you have malabsorption syndrome, you’ll likely experience additional symptoms such as pale, greasy, foul-smelling stools. Changes in energy levels and unintentional weight loss are also common.

Inflammatory bowel disease (IBD)

Inflammatory bowel disease (IBD) refers to two conditions: Crohn’s disease and ulcerative colitis.

Both are characterized by inflammation of the intestine, although these two conditions can affect different parts of the gastrointestinal tract. If you have been noticing unintentional weight loss, blood in your stool, or other systemic symptoms, your diarrhea may be a sign of developing IBD.

When to see a doctor about diarrhea

Diarrhea is a frustrating and sometimes concerning symptom. Knowing when to see your doctor or go to the emergency room can help prevent any negative health effects.

You should see a doctor if:

• Your symptoms occur more frequently, or the volume of your bowel movements continues to increase despite treatment.
• You notice weight loss.
• You have significant changes in appetite.
• You experience significantly worsening abdominal pain.
• You have any of the following:
  • Symptoms beginning after 50 years of age.
  • Rectal bleeding or melena (black, tarry stools).
  • Pain or diarrhea during the night.
  • Fever.
  • A close relative with IBD or colorectal cancer.

You should go to the emergency room if:

• You vomit blood.
• You notice bright red blood in your bowel movements.
• You experience loss of control of your bladder or bowel.
• You experience sudden dizziness that does not resolve.
• You experience ongoing palpitations—the sensation of a racing heart that does not resolve.
• You are unable to keep anything down due to ongoing nausea or diarrhea, including food and liquids.
• You develop seizures.

Question to ask your doctor about diarrhea

• Is there any need for blood work, stool studies, or other labs to assess my diarrhea?
• Is there a need for any imaging, such as CT or MRI?
• Should I discontinue metformin to see if it’s related to my symptoms?
• What medications should I switch to if I stop taking metformin?

How to treat, manage, or get relief from diarrhea while taking Metformin

Now that we’ve discussed potential causes of your diarrhea, including metformin use, here are some treatment options you can try at home.

Medication change

Whether you’ve recently started taking metformin, had a recent dose change, or have been taking metformin for a while, your diarrhea may be due to the medication.

Uncontrolled diabetes can lead to serious long-term complications worse than diarrhea. Therefore, before choosing to stop taking metformin, talk to your doctor to see if this is a safe option for you. You’ll want to discuss what medication to take instead.

Lactose-free diet and other dietary modifications

If you notice that your diarrhea begins or worsens after eating a specific food, it may help to eat less of that food or cut it out completely. It’s helpful to keep a diary of what you eat, how your symptoms respond, weight fluctuations, and other relevant details to help determine whether something in your diet is causing diarrhea.

Fiber supplements, Pepto-Bismol

While taking additional medications to address the side effects of another may feel like a bit much, there are safe over-the-counter medications that may provide relief. Adding more fiber to your diet can help form more solid stools. You can do this by eating more fiber-rich foods, such as beans, whole grains, certain fruits and vegetables, and nuts.

You can also try using medications like Pepto-Bismol, but keep in mind that Pepto-Bismol can make your stool dark in color.

Frequently asked questions: Metformin and diarrhea

Here are some common questions regarding metformin use and diarrhea:

Does diarrhea from metformin lead to weight loss?

Although diarrhea can lead to weight loss, diarrhea caused by metformin can be slightly different. Because metformin is a medication used to help your body regulate blood sugar levels, the weight loss you experience may be reflective of improved blood glucose monitoring and control.

Can polycystic ovarian syndrome (PCOS) play a role in experiencing diarrhea while on metformin?

Because metformin can help address weight concerns, it has been used as a medication to help patients with PCOS.

Although PCOS is not associated with higher rates of diarrhea while on metformin, those with PCOS taking the medication may experience diarrhea as a side effect.

How long does diarrhea typically last while on metformin?

Although every patient is different, diarrhea caused by metformin can last anywhere from a few days to a few weeks. If you notice that your symptoms are getting worse over time, speak with your doctor.

Final thoughts: Metformin doesn’t fix everything

While metformin is a wonderful and safe drug that works, like every medication, it can have side effects like diarrhea. If you’re experiencing diarrhea while taking metformin, your symptoms should resolve on their own within a few days or weeks. If they persist or worsen, consult a healthcare provider to learn what steps to take next. Before starting any new medication, speak with your primary care provider about the possible side effects so you can better educate yourself and take control of your health.

Sources

Flaherty, Robert J. “Case Report: Late-Onset Metformin-Associated Diarrhea.” American Fam Physician. 2023;108(2), https://www.aafp.org/pubs/afp/issues/2023/0800/letter-metformin-associated-diarrhea.html. Accessed 17 November 2024.

GRADE Study Research Group et al. “Glycemia Reduction in Type 2 Diabetes - Glycemic Outcomes.” The New England Journal of Medicine vol. 387,12 (2022): 1063-1074. doi:10.1056/NEJMoa2200433

Robyn. “Bristol Stool Chart.” Continence Foundation of Australia, 9 Feb. 2024, www.continence.org.au/bristol-stool-chart.