Does metformin cause diarrhea?

In this article:

• Does metformin cause diarrhea?
• Duration
• Prevention
• Managing diarrhea from metformin
• When to see a doctor

In this article

• Does metformin cause diarrhea?
• Duration
• Prevention
• Managing diarrhea from metformin
• When to see a doctor

Metformin is a commonly prescribed medication used together with diet and exercise to manage blood glucose levels in people with Type 2 diabetes. It works by reducing the amount of glucose the liver makes, by lowering the amount of glucose absorbed from food, and increasing glucose uptake into the body’s cells. While it is often referred to by its brand names, Glucophage, Fortamet, or Glumetza, metformin is a generic medication that comes as an oral tablet and solution. The tablet comes in both an immediate-release and extended-release form.

Although it is an effective and popular treatment option for diabetes, metformin can cause gastrointestinal side effects in patients who take it–especially when it’s first started. These include diarrhea, nausea, vomiting, abdominal discomfort, and gas, with diarrhea being the most common side effect. 

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Does metformin cause diarrhea?

While metformin is considered one of the safest drugs for diabetes mellitus, digestive system effects can occur in up to 75% of people who take metformin. Diarrhea is more common with the immediate-release form compared to the extended-release form. In clinical trials, diarrhea occurred in 53.2% of people taking immediate-release metformin and in 10% of people taking extended-release metformin. 

Why does metformin cause diarrhea?

Diarrhea is most common when people first start taking metformin. However, the reason why metformin causes diarrhea isn’t entirely clear. 

Metformin has several effects on the gut, including:

• Increasing glucose uptake and lactate production.
• Increasing glucagon-like peptide-1 (GLP-1) and bile acids inside the intestine.
• Changing the gut’s microbiome.

By increasing bile acids, metformin may have an osmotic effect, drawing water into the intestine and leading to diarrhea. It may also alter the gut microbiome–including fungi, bacteria, and viruses–which may cause diarrhea. Metformin also increases the release of serotonin in the intestines, which has been associated with nausea, vomiting, and diarrhea. 

How long does diarrhea from metformin last?

For most people, diarrhea is most common when you first start taking metformin or after a delay of a few weeks. Luckily, it’s less likely to occur as treatment goes on. With that being said, there have been some reports of chronic (long-term) cases of diarrhea, even after several years of stable dosing. 

If you develop severe diarrhea or diarrhea that won’t go away while taking metformin, talk with a healthcare professional. They can provide recommendations for managing diarrhea and help determine whether you should continue treatment with metformin. 

Preventing metformin diarrhea

Because diarrhea is a fairly common problem with metformin, prevention is key. Digestive side effects such as nausea, vomiting, and diarrhea may be more likely if you take metformin on an empty stomach. Therefore, metformin should be taken with a meal. Another way to minimize the risk of gut-related side effects is to increase your dose slowly. For this reason, your healthcare will likely start you on a low dose of metformin and increase the dose slowly over time. 

Managing diarrhea from metformin

Although most cases of diarrhea will resolve on their own over time, there are some ways you can manage your symptoms. 

• Switching to the extended-release form. In studies, diarrhea was much more common with the immediate-release (IR) tablet than with the extended-release (ER) tablet. This may be because the ER form releases the drug more slowly over time compared to the IR form. While healthcare providers usually start people on IR metformin initially, if the medication is well tolerated, they can seamlessly switch you to the ER form. 

• Dosage adjustment. As discussed above, one way to minimize gastrointestinal side effects is to increase your dosage slowly over time. This gives your body time to adjust to the medication. Doctors will likely start you on a low dose of metformin and gradually raise it until you reach the dose that best manages your blood sugar levels. 

• • Switching medications. If you’re experiencing persistent and worsening diarrhea from metformin, it’s important to talk to your healthcare provider. They can help determine if metformin is the cause and, if so, if it’s safe for you to continue taking the drug. In some cases, you and your healthcare provider may decide that the benefits of metformin aren’t outweighing the risks. If this is the case, switching you to another diabetes medication may be helpful. 

• Antidiarrheal medications. In certain cases, metformin-induced diarrhea can be treated with antidiarrheal medications. However, these medications aren’t safe for everyone, so it’s best to consult a pharmacist or other healthcare provider before you take one. Over-the-counter and prescription medications, such as Imodium (loperamide) and Lomotil (diphenoxylate/atropine), are available to treat diarrhea. 

When to see your healthcare provider

If you have diarrhea that lasts longer than a few weeks or diarrhea that’s accompanied by severe symptoms such as bloody stools, fever, or severe abdominal pain, it’s a good idea to talk with your healthcare provider. They can help determine the cause, and you can discuss the best ways to manage your symptoms together. These may include adjusting your metformin dosage, switching to the extended-release form, or taking antidiarrheal medications. If none of those strategies work, your healthcare provider can prescribe an alternative medication.