Does metformin cause constipation?

In this article:

• Metformin and constipation
• Why does it cause constipation?
• Managing constipation
• When to see a doctor

In this article

• Metformin and constipation
• Why does it cause constipation?
• Managing constipation
• When to see a doctor

If you take metformin for Type 2 diabetes, you’re not alone. It’s one of the most commonly prescribed and most effective medications for managing blood sugar levels. While it’s generally well tolerated, it can sometimes affect your digestive system. If you’re noticing constipation or other gastrointestinal issues and wondering whether metformin might be the culprit, here’s what you need to know.

Can metformin cause constipation?

Metformin is a biguanide medication used as a first-line treatment for Type 2 diabetes. It reduces the liver’s glucose production, decreases intestinal glucose absorption, and improves insulin sensitivity. Beyond blood sugar control, research shows that metformin may also support cardiovascular health. It’s prescribed off-label (a non-FDA-approved use) for conditions like polycystic ovary syndrome (PCOS) or antipsychotic-related weight gain. It’s available in several brand-name and combination forms, including Glucophage, Glucophage XR, Fortamet, Riomet, Janumet (metformin and sitagliptin), Synjardy (metformin and empagliflozin), and Jentadueto (metformin and linagliptin).

Like many medications, metformin can affect the gastrointestinal (GI) tract. Studies suggest it may alter gut microbiota, which may explain why many patients report digestive symptoms. In a meta-analysis of 71 randomized controlled trials, up to 20% of people taking metformin reported GI side effects. Some research suggests the rate may be much higher—potentially up to 75%.  GI side effects are more common with immediate-release versions compared to extended-release formulations.

Common signs of constipation include: 

• Infrequent bowel movements (fewer than three per week)
• Straining or abdominal pain
• Hard or lumpy stools
• A feeling of incomplete evacuation
• A sensation of blockage in the rectum

However, when it comes to metformin, constipation is actually less common than other GI symptoms.

“While metformin is a common source of gastrointestinal (GI) issues, including diarrhea, nausea, and stomach pain, the good news is it is much less likely to be associated with constipation,” says Rachel Pessah-Pollack, MD, an endocrinologist and clinical professor at NYU Langone Health. 

Why does metformin cause constipation?

Constipation is already common among people with diabetes, due in part to changes in nerve function. Research shows it is one of the most frequently reported lower-GI symptoms in individuals with diabetes. Damage to the autonomic and enteric nervous systems (often related to long-term high blood sugar) can slow intestinal motility and contribute to constipation.

Medications can add another layer to the problem. “Metformin is more known for causing diarrhea, but like many medications, including other diabetes medications like Ozempic, some patients experience constipation with metformin,” says Bryan Curtin, MD, a gastroenterologist and director of The Center for Neurogastroenterology and GI Mobility in Baltimore, Maryland.

However, the mechanism isn’t fully understood. “Some theories discuss effects on gut motility, balance of bile acids in the GI tract or possibly the gut microbiome, but these are all theories,” Dr. Curtin adds. These factors may also contribute to or exacerbate constipation:

• Dehydration: A lack of adequate fluid intake is strongly linked to constipation. One study noted that higher dietary moisture intake is associated with a lower risk of constipation.
• Dietary choices: Low fiber intake is a major contributor to sluggish, constipated bowels. Fiber supports gut motility, improves blood sugar control, increases insulin sensitivity, and benefits cardiovascular and metabolic health.
• Lifestyle habits: Limited physical activity makes constipation worse, especially in people already predisposed due to diabetes. Exercise helps strengthen muscles involved in defecation and supports overall gut movement.
• Other medications: Several drugs are known to cause constipation, including antidepressants, anticholinergics, calcium-channel blockers, antispasmodics, sedatives, anticonvulsants, and aluminum-containing antacids.

Managing constipation while taking metformin

If you’re noticing symptoms of constipation while on metformin, several simple strategies may help you feel better and restore regularity.

Increase your fiber intake gradually

A fiber-rich diet is recommended for diabetes care, and it can also help ease constipation. Try adding more legumes, whole grains, and non-starchy vegetables to your meals. Just increase slowly: the CDC advises increasing fiber intake gradually to avoid worsening constipation or triggering bloating, gas, or abdominal discomfort.

Watch out for certain foods and supplements

Dairy products, such as cheese and milk, can be constipating when consumed in large amounts. Certain supplements, especially iron and calcium, may also slow down digestion. If you’re unsure whether a supplement is necessary, check in with your healthcare provider.

Stay hydrated

Dehydration is a common cause of constipation. Aim to drink adequate fluids throughout the day and consider adding foods with high water content, such as cucumbers, watermelon, cantaloupe, and strawberries. Try not to drink alcohol or other dehydrating beverages.

Get moving

Regular movement supports healthy digestion. Some studies suggest that aerobic exercise, in particular, may help relieve constipation. Even moderate activities like brisk walking can make a difference.

Try over-the-counter remedies

If lifestyle changes aren’t enough, an OTC laxative may help. “If these are ineffective, they can use Miralax over the counter,” says Dr. Curtin. Always seek medical advice for persistent symptoms or if you are considering new medications.

When to talk to your healthcare provider about constipation

Mild or occasional constipation often improves with simple lifestyle adjustments. However, if your symptoms worsen or become persistent or you have blood in your stool, it’s important to reach out to your healthcare provider.

“If your constipation is associated with other symptoms, such as vomiting, stomach pain, or dehydration, this requires urgent medical attention and further evaluation,” Dr. Pessah-Pollack says. “Constipation that continues or becomes more severe despite diet modifications and hydration requires a visit with their doctor for further evaluation.”

Although uncommon, metformin can also lead to more serious complications, such as increased risk of lactic acidosis, a buildup of lactic acid in the bloodstream. Symptoms may include extreme fatigue, weakness, or lightheadedness. If you experience these signs, contact a healthcare professional right away. Fatigue may also indicate anemia or vitamin B12 deficiency, another possible issue in long-term metformin users, so evaluation is important.

Bottom line

Metformin is a well-established, inexpensive, effective treatment for Type 2 diabetes and offers several additional health benefits. For most people, it causes few or no side effects. However, if you’re experiencing constipation or other digestive symptoms you believe may be related to metformin, let your healthcare provider know. They can help identify the cause, recommend strategies to mitigate side effects of metformin, or discuss whether a different treatment approach might be more suitable.