Why Does Metformin Cause Diarrhea?

Metformin can cause diarrhea as a common side effect. While most side effects resolve after the first several days of taking metformin, for some people it may last longer.

Metformin helps get rid of excess glucose from the body. Part of it is removed through the intestines. This process can be part of the reason why diarrhea is a common side effect.

In this article, we’ll explore how to manage the side effects of metformin and how to know when you should see a healthcare provider.

Why Does Metformin Cause Diarrhea?

Metformin can be a highly effective medication for managing elevated blood glucose levels. It blocks the liver from making more glucose.

Lactic acid is produced as a byproduct of the liver’s inaction, and excess glucose is removed from the body via the intestines.

Since this is not a normal route for excess glucose it can change the consistency of typical bowel movements.

Glucose elimination via the intestines also leads to an increase in lactic acid, which is a gut irritant. Lactic acid in the intestines can also contribute to diarrhea from metformin.

Metformin can also alter the gut microbiome of people who take it. In some cases, the effect can be a positive change, leading to better short-chain fatty acid production.

In other cases, some types of bacteria that thrive under metformin may be part of the cause of diarrhea.

While diarrhea is a much more common side effect, constipation is also possible.

When participants of one study compared types of gastrointestinal symptoms, constipation was actually found to be more severe than diarrhea.

Most diarrhea that is caused by metformin will only be a short-term side effect.

In some cases, but far less often, metformin can be a cause of chronic diarrhea long after the body has adjusted to the medication.

Chronic diarrhea is more than just a few days, but lasts several weeks at a time. In studies done on metformin causing chronic diarrhea, it typically resolved as soon as metformin was discontinued.

How Long Does Diarrhea from Metformin Last?

The typical side effect of diarrhea that is caused by metformin does not last long-term.

It typically resolves within a few days or few weeks once the body adjusts to the medication.

If diarrhea from metformin does last longer, your healthcare provider can help to determine if it is being caused by metformin or something else.

In more rare cases, excess build-up of lactic acid can result in lactic acidosis, a potentially life-threatening condition.

Managing Metformin Diarrhea

There are ways to decrease the gastrointestinal side effects that metformin can have on the gastrointestinal system.

A healthcare provider may do the following:

• Start you on a low dose or decrease your dosage
• Have you take metformin at meal times
• Prescribe extended-release metformin so that it is taken less frequently, which could minimize side effects

There are also ways that you can address the short-term side effects to find comfort while your body adjusts to the medication:

• Stay hydrated: Diarrhea can deplete fluids, which can make other signs and symptoms worse.

• Eat the BRAT diet: Bananas, rice, apples, tea, and toast are a basic diet that can decrease strain on the gastrointestinal tract. It is often recommended for other types of diarrhea. If you are taking metformin for diabetes, make sure that you also eat protein and follow your other dietary instructions.

• Fiber: In some cases, diarrhea could be triggered from not having enough fiber in the diet. Fiber is important for helping to control blood glucose and also supports weight loss. High-fiber foods include whole grains, fruits, and vegetables.

If your diarrhea is severe, your medical provider may suggest taking anti-diarrheal medication. They may also recommend stopping metformin for a short period of time to see if the diarrhea resolves.

Other Metformin Side Effects

Common side effects of metformin are short-term and mild.

In addition to diarrhea, they include:

• Headache
• Nausea and vomiting
• Weight loss
• Bloating
• Gas
• Bad (metallic) taste in mouth

Managing Side Effects

Your medical provider will start you on a low dose to give your body time to adjust to the medication. In most cases, this can help to minimize side effects.

Taking metformin with meals can help to decrease how strongly it impacts gastrointestinal function.

Metformin works to support balanced blood sugar in addition to diet, lifestyle, and exercise. Eating a well-balanced diet can help to improve general wellness and supports better digestion.

When to See a Medical Provider

If you are taking metformin and the side effects are unmanageable or are getting worse, your healthcare provider can help create a plan to find relief.

They may also prescribe an alternative to metformin if you are struggling to tolerate it.

There are many FDA-approved alternatives to metformin. Some include sodium-glucose co-transporter 2 (SGLT2) inhibitors like canagliflozin (Invokana) and dapagliflozin (Farxiga). 

Instead of eliminating glucose via the intestines, like metformin, these medications decrease glucose levels by eliminating via the kidneys and urine.

Whether you have recently started taking metformin or have been taking it a long time, diarrhea is an unpleasant side effect. You can speak with a healthcare provider in the K Health app, right from your home.

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