Does Metformin Cause Diarrhea? Here’s What You Should Know

imed22/ May 21, 2025/ General/ 0 comments

If you’re taking metformin for type 2 diabetes and have started noticing changes in your digestive health, particularly diarrhea, you’re not alone. Diarrhea is one of the most common side effects reported by patients on metformin therapy. While this drug is highly effective in lowering blood sugar and supporting weight loss, it can also cause discomfort in the gastrointestinal tract for some individuals.

In this article, we’ll take a deep dive into the connection between metformin and diarrhea, including why it happens, how long it lasts, and what you can do to manage or prevent it.

Understanding Metformin: A Common Diabetes Medication

Metformin is widely prescribed as a first-line treatment for type 2 diabetes. It works by improving the body’s response to insulin and reducing the amount of glucose produced by the liver. It also decreases the absorption of intestinal glucose and increases insulin sensitivity.

Despite being a common drug in diabetes care, metformin isn’t without side effects. Gastrointestinal symptoms such as nausea, vomiting, bloating, and especially diarrhea, are frequently reported, especially when first starting treatment.

Why Does Metformin Cause Diarrhea?

One of the reasons diarrhea occurs in people who take metformin is due to how the drug interacts with the gastrointestinal tract. Metformin is not absorbed well by the body, meaning much of it stays in the gut. This interaction affects:

• The gut microbiome
• Bile acids
• Intestinal glucose
• Food and meals

Metformin may alter the natural balance of bacteria in the gut, influence bile acid metabolism, and reduce the absorption of glucose in the intestines. Taking metformin on an empty stomach or with certain types of food may also increase the chances of stomach upset. This collection of effects helps explain why diarrhea is a common side effect for some patients starting or continuing metformin therapy.

How Common Is Diarrhea From Metformin?

Studies and patient reports suggest that diarrhea affects between 10% and 25% of those who take metformin. For most people, this side effect is mild and temporary. However, in some cases, it becomes persistent or severe, leading to what’s termed metformin induced chronic diarrhea.

A literature review and multiple case report studies have also described late onset chronic diarrhea in patients who had previously tolerated metformin well for years. This condition, while relatively rare, does occur and may be difficult to diagnose unless the connection to the medication is recognized.

Chronic Diarrhea and Weight Loss: What’s the Link?

Some patients experience both chronic diarrhea and weight loss while taking metformin. While weight loss is often considered a positive effect in patients with type 2 diabetes or obesity, when combined with persistent diarrhea, it can become a concern. Diarrhea and weight loss can lead to dehydration, loss of essential nutrients, and reduced quality of life.

It’s important to distinguish whether the weight loss is intentional (through diet and exercise) or a side effect of ongoing gastrointestinal issues related to metformin.

Is Metformin Always to Blame?

Not necessarily. While metformin is a common drug causing diarrhea, other conditions may also contribute to chronic digestive symptoms. For instance:

• Irritable bowel syndrome (IBS)
• Infections
• Other medications
• Lactose intolerance
• Dietary triggers

If you’re experiencing symptoms like diarrhea, nausea, or stomach cramps after meals, talk to your doctor to rule out other causes before assuming metformin is responsible.

When Does the Diarrhea Start, and Will It Go Away?

For most patients, diarrhea starts within the first few weeks of beginning treatment. It often improves as the body adjusts to the medication. However, in some cases, patients report symptoms persisting for months or even years.

In uncommon time metformin induced chronic diarrhea, patients may develop symptoms after being on the medication for an extended period. This effect at an uncommon time can make it more difficult to connect the dots between the drug and the symptoms.

Can You Prevent Diarrhea While Taking Metformin?

Yes, there are steps you can take to prevent diarrhea or at least reduce its severity.

Start with a Low Dose

Many doctors recommend starting with a small dose and increasing it gradually to allow your body to adjust.

Always Take Metformin With Food

Taking metformin with meals helps buffer the drug’s effects on the stomach and intestines, making side effects like diarrhea less likely.

Ask About Extended Release Formulation

The extended release version of metformin (sometimes labeled as ER or XR) is designed to release the medication slowly over time. It is often associated with fewer gastrointestinal side effects compared to the immediate-release version.

Monitor Your Diet

Avoid high-fat, greasy, or overly sugary foods while adjusting to metformin. These can irritate the digestive system and worsen symptoms.

What to Do if Diarrhea Persists

If your symptoms continue despite these efforts, don’t suffer in silence. Some possible steps to take include:

• Talk to your doctor about switching to the extended release formulation
• Evaluate whether other medications might be causing diarrhea
• Consider a temporary break to see if symptoms resolve
• Ask whether you should stop taking metformin and explore alternative treatments

Never stop or change your medication on your own without medical guidance.

A Look at the Research

Some studies in Clin Diabetes and other journals have explored the long-term effects of metformin on the gastrointestinal tract. Findings indicate that while most side effects are mild and self-limited, late gastrointestinal complications such as metformin induced chronic diarrhea can have a real impact on patients’ lives.

A case report by Liu SL and others noted that weight loss after years on metformin combined with worsening diarrhea could signal the need for reevaluation of treatment.

FAQs

Can metformin cause diarrhea years after starting it?
Yes, in rare cases, late onset chronic diarrhea can occur even in patients who have taken metformin for years without issue.

How long does metformin diarrhea last?
For most people, it lasts a few weeks and resolves as the body adjusts. If it continues, speak with your doctor.

Is there a way to prevent diarrhea when starting metformin?
Starting with a low dose, taking the medication with food, and switching to an extended-release version can help prevent diarrhea.

Should I stop taking metformin if I have chronic diarrhea?
Do not stop the medication without talking to your doctor. There may be ways to adjust your treatment instead.

Does diarrhea from metformin help with weight loss?
While diarrhea and weight loss may occur together, it’s not a healthy or intended method of weight loss and should be addressed.

Let your healthcare provider know if you’re experiencing any troubling side effects from metformin. Personalized care is the key to successful diabetes management.

Final Thoughts: Managing Your Diabetes Without the Discomfort

Metformin remains a cornerstone in the treatment of type 2 diabetes, offering benefits like better blood sugar control and support for weight loss. However, it is also known as a common drug causing a common side effect: diarrhea.

The good news is that with careful monitoring, dosage adjustments, and possibly switching to the extended release version, most patients can continue taking metformin without persistent discomfort.

If you are experiencing diarrhea that doesn’t go away, affects your daily life, or leads to other symptoms like fatigue or weight loss, speak to your healthcare provider. Together, you can develop a plan that keeps your diabetes in check while also supporting your gut health.

References:

https://www.goodrx.com/metformin/can-metformin-cause-diarrhea

https://www.healthline.com/health/diabetes/metformin-side-effects

https://www.verywellhealth.com/does-metformin-cause-diarrhea-8686560

https://www.drugs.com/medical-answers/why-metformin-cause-diarrhea-3574975/