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Tuesday, January 25, 2022

Can Metformin Cause Diarrhea?


Metformin is a well-known, affordable, and widely used drug to help manage type 2 diabetes and achieve better blood glucose control. 

Metformin is used to help lower blood sugar levels, improve hba1c readings, and can help patients lose weight. 

While common, clinical side effects, such as nausea, vomiting, gastrointestinal issues, and diarrhea are normal and expected at the start of treatment, chronic diarrhea after long-term Metformin use is less widely studied but has occurred in patients. 

Is Metformin the cause? What’s the solution? This article will study this lesser-known side-effect of Metformin, the risks associated with chronic diarrhea after Metformin use, and what to do about it. 

Metformin for diabetes 

Metformin is an oral diabetes drug that’s been in use since the 1950s, and is one of the most popular diabetes drugs on the planet, with physicians writing over 120 million Metformin prescriptions annually. 

The drug is used to help patients with type 2 diabetes better manage their condition and can help obese patients lose weight more easily, even if they don’t have diabetes. 

Metformin is affordable in the United States, and virtually all health insurance plans cover the drug. It is usually taken once or twice per day with meals. 

Its suggested use is in conjunction with an improved diet and exercise routine. Metformin lowers blood glucose levels by slowing the release of glucose from the liver while increasing insulin sensitivity by lowering the amount of sugar you absorb from food. 

Most people find the drug tolerable and easy to fit into their lifestyles to improve health outcomes, but some experience adverse effects. 

Common side effects 

Common, and usually mild, side effects of Metformin may include: 

  • Stomach cramps
  • Nausea
  • Vomiting
  • Diarrhea
  • Stomachache
  • Suppressed appetite 
  • Weight loss 
  • Low blood sugar (in people who use exogenous insulin)

More information on side effects can be found in our article: Metformin Side Effects: What You Need to Know.

According to Diabetes, Obesity, and Metabolism, many of the initial gastrointestinal side effects that patients experience can appear immediately after one’s initial dose, with most going away after the body recalibrates to the medicine within a few weeks. 

However, not all symptoms may go away, lending to Metformin’s low adherence rates

Chronic diarrhea can be one of those, at best pesky, and, at worst dangerous, side effects that never goes away once someone starts a Metformin regimen. 

Can Metformin cause chronic diarrhea? 

Chronic diarrhea is defined as loose stools that last at least four weeks, with between three to four loose stools per day. 

A study out of the American College of Clinical Pharmacy found that yes, this can happen, and it’s actually more common than one would think. After a patient’s initial recalibration period, usually distressing side effects such as nausea, vomiting, and diarrhea fade away, but sometimes, after years of stable Metformin treatment, the body may start to respond negatively to treatment once again. 

In one case, the person started producing what the researchers describe as, “nausea, abdominal cramping, and explosive, watery diarrhea that occasionally caused incontinence”, after several years of consistent Metformin treatment. 

The patient’s gastrointestinal symptoms went away once treatment ceased. 

Another study, in the Journal of Endocrinology and Metabolism, found that late-onset, chronic diarrhea occurred in someone who had previously been taking Metformin for over 5 years, with no previous complications or side effects. 

The diarrhea was painless, but severe, with no other underlying cause. The diarrhea completely went away after the Metformin treatment stopped. 

In both of these patient cases, the exact trigger of the sudden diarrhea is unknown; Metformin seems to be well-tolerated in some patients until it’s not. 

People experiencing polypharmacy may be at increased risk for chronic diarrhea from Metformin use, due to interactions between many types of drugs. 

However, stopping one or more drugs may cause complications for people also managing other health conditions, such as diabetes, which becomes much harder to manage without the Metformin treatment.

Other diabetes-related causes of diarrhea

Metformin isn’t the only diabetes-related cause of diarrhea. It’s important to rule out other causes of diarrhea before changing your diabetes medication

Diabetic neuropathy from persistent high blood glucose levels

Diabetic neuropathy that affects the digestive system is called diabetic enteropathy. This form of nerve damage to the digestive tract can impact not only the frequency of bowel movements, but the consistency as well, oftentimes causing diarrhea. 

Bacterial overgrowth

Diabetes complications, like gastroparesis, can cause the movement of foods and beverages through one’s digestive system to slow down, which creates the ideal environment for bacteria to grow. This slowing of the digestive system can cause everything from constipation to diarrhea. Check with your doctor if you think you have gastroparesis. 

Over-use of artificial sweeteners

Artificial sweeteners, such as Equal, Splenda, or Sweet’N’Low can make enjoying sweeter treats easier on your diabetes, but can wreak havoc on the digestive system, often causing diarrhea. 

Artificial sweeteners are poorly digested by the gastrointestinal tract and are commonly known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols). If you enjoy artificial sweeteners, make sure to use them sparingly. 

The dangers of chronic diarrhea 

The dangers of persistent diarrhea can range anywhere from a mild inconvenience, to becoming completely house-bound, unable to exercise, work, or function in society. 

Beyond lifestyle issues, however, chronic diarrhea can be extremely detrimental to one’s health, too. Some complications of chronic diarrhea are:

  • Malnutrition/malabsorption of nutrients 
  • Dehydration
  • Excessive thirst 
  • Excessive weight loss 
  • Fatigue
  • Dizziness
  • Lethargy 
  • Dark urine
  • Low blood sugar 
  • Inability to exercise
  • Social isolation
  • Embarrassment
  • Skin irritation 

If you’re experiencing chronic diarrhea and have any of the aforementioned health complications and you live with diabetes, seek immediate medical attention or contact your doctor right away to get help. 

How to avoid or reduce the risk of diabetic diarrhea from Metformin

Extended-release tablets

Studies have shown that patients who experience diarrhea using immediate-release Metformin may find relief when switching to extended-release Metformin tablets, while still experiencing the benefits of the medicine. 

These formulations spread the absorption of Metformin throughout the entire gut, reducing local concentrations of the drug and increasing tolerability. 

Take your Metformin with meals

Taking your Metformin with meals has been shown to reduce the risk of diarrhea. Focus on a higher protein meal or snack when taking it. Never take Metformin on an empty stomach. Metformin is usually better tolerated in the evening, so taking it with dinner is best. 

Never take more than is prescribed 

Start your Metformin on a low dose, and do not increase your dose without the guidance of your doctor. If you start to feel nausea and experience diarrhea, contact your doctor about lowering your dose until you build tolerance again. 

Stop taking Metformin for a few weeks 

Giving your gut time to heal with a few weeks’ break away from the medicine can help stop diarrhea and prevent it from coming back. Always talk to your doctor before you stop taking Metformin.

Look into alternative treatment options 

If none of the aforementioned strategies help alleviate your diarrhea, and it’s negatively affecting your quality of life, talk to your doctor about stopping Metformin, and look for alternative treatments to manage your diabetes instead. 

Treating chronic diarrhea 

Patients experiencing long-term diarrhea should seek professional medical attention, especially if they live with diabetes. 

However, if you wish to treat your condition at home, or your symptoms are not severe, some of the following treatments may offer temporary relief:

  • Drinking plenty of water and getting electrolytes (Gatorade or coconut water) to replenish lost salts and prevent dehydration 
  • Taking an over-the-counter Bismuth to stop the diarrhea, such as Pepto-Bismol 
  • Eating a higher-fiber diet to firm up the stools 
  • Taking a daily fiber supplement 
  • Taking anti-diarrhea medications, such as loperamide (Imodium). Only ever take the recommended dose, as exceeded that has led to serious heart complications in some patients 

If your diabetic diarrhea is severe enough and it’s negatively affecting your quality of life, talk with your doctor about lessening or even weaning off your dose of Metformin.


Late-onset, chronic diarrhea seems to be a more common (although less talked about!) complication of long-term Metformin use, especially in people experiencing polypharmacy (multiple medications treating multiple conditions at once). 

Minor lifestyle modifications may help relieve some of the complications of late-onset, Metformin-induced diarrhea, such as drinking plenty of fluids and electrolytes, taking over-the-counter medications, eating a high fiber diet (including plenty of fruits and vegetables), and including a daily fiber supplement into your daily routine. 

If the chronic diarrhea does not improve, and the complication is not quickly assessed and recognized, this can lead to often unnecessary and invasive medical procedures and clinical investigations, additional medications (like prescription anti-diarrhea medications), discomfort, embarrassment, and major lifestyle modifications (some of which may be restrictive, such as an inability to leave the home, for example). 

If no other causes of chronic diarrhea are present, and the chronic diarrhea is persistent and severe, it may be wise to talk with your doctor about lessening your dose or weaning yourself off of your Metformin completely. 

Your doctor may recommend trying an alternative medication to better manage your diabetes and blood sugar levels. As studies have shown that stopping Metformin treatment almost immediately alleviates late-onset, chronic diarrhea. 

Always work with your diabetes care team to assess the right treatment options for you personally that will fit your lifestyle while still achieving your health goals. 

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