Why does metformin cause diarrhea?
Metformin is a widely prescribed medication for type 2 diabetes, but one of its most common side effects is diarrhea. Some reasons metformin causes diarrhea include microbiome changes in the gut, hormonal effects, and changes in the intestine that cause increased water in the stool. Understanding why metformin causes diarrhea can help patients manage symptoms and make informed decisions about their treatment.
How Common is Diarrhea From Metformin?
According to the manufacturer, about 53% of people taking metformin immediate-release tablets experienced diarrhea in one clinical study. In another study, 10% of people taking metformin extended-release tablets reported diarrhea as a side effect.
Why Does Metformin Give You Diarrhea?
Diarrhea can happen when your dose of metformin is raised too quickly, or if you take too high of a dose. It’s not fully clear why metformin causes diarrhea as a side effect. Researchers believe it could be due to the following reasons:
- Gut Microbiome Changes: Metformin alters the balance of bacteria in the gut, increasing certain strains that can lead to looser stools.
- Bile Acid Malabsorption: The drug may interfere with the reabsorption of bile acids, which can draw water into the colon and cause diarrhea.
- Inhibition of Intestinal Transporters: Metformin inhibits the sodium/hydrogen exchanger 3 (NHE3) in the intestines, leading to increased water in the stool.
- Hormonal Effects: It can increase levels of GLP-1, a hormone that stimulates the gut, and may also affect serotonin and histamine, further promoting bowel movements.
Think of metformin as changing the plumbing and water flow in your digestive system, making it easier for water to pass through and resulting in loose stools.
Chronic and Late-Onset Diarrhea with Metformin
While many people experience diarrhea soon after starting metformin, some develop symptoms months or even years later. This delayed reaction can be confusing and is sometimes misdiagnosed as irritable bowel syndrome (IBS).
What to Watch For
- Chronic Symptoms: Ongoing loose stools or urgency that persist beyond the first few weeks of treatment. Weight loss is another red flag.
- Late-Onset Cases: Diarrhea developing after years of stable dosing.
- Misdiagnosis Risk: Symptoms may be mistaken for IBS or other gastrointestinal conditions.
When to Suspect Metformin
- If diarrhea starts or worsens after increasing the dose.
- If symptoms improve when metformin is stopped or the dose is reduced.
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How Long Does Diarrhea Caused By Metformin Last?
The amount of time it takes for diarrhea caused by metformin to go away is different for everyone. It generally goes away after a while, as your body gets used to the medication. If it lasts more than a few weeks, make sure to tell your doctor. Also let your doctor know if the diarrhea goes away and then comes back again.
How to Stop Metformin Diarrhea: Management and Prevention
Managing metformin-induced diarrhea is possible with a few practical strategies. Here are the most effective approaches:
- Gradual Dose Titration: Start with a low dose and increase slowly to allow the gut to adjust.
- Extended-Release (ER) Formulations: Switching to ER versions can reduce diarrhea in up to 90% of affected patients.
- Take with Food: Always take metformin with meals to minimize stomach upset and loose stools.
- Dietary Adjustments: Avoid high-fiber or high-fat foods and artificial sweeteners that may worsen diarrhea.
- OTC Antidiarrheals: Short-term use of medications like loperamide can help, but consult your doctor first.
If diarrhea is severe or persistent, discuss alternative medications or further testing with your healthcare provider.
Frequently Asked Questions (FAQ) About Metformin and Diarrhea
How long does metformin diarrhea last?
For most people, diarrhea improves within a few weeks as the body adjusts. However, some patients may experience persistent symptoms.
Does metformin diarrhea go away on its own?
Yes, for many, symptoms resolve with time or dose adjustments. If not, switching to an extended-release formulation or other management strategies can help.
What percentage of people get diarrhea from metformin?
Estimates suggest that 50% of patients experience some degree of diarrhea, and up to 6% may discontinue the drug due to side effects.
Can metformin cause explosive diarrhea or urgency?
Yes, some patients report sudden and severe urges to use the bathroom, especially soon after starting or increasing the dose.
This is not all the information you need to know about metformin for safe and effective use and does not take the place of your doctor’s directions. Review the full patient medication guide and discuss this information and any questions you have with your doctor or other health care provider.
References
- Ascend Laboratories, LLC. (2022). Metformin package insert. Accessed September 2, 2023. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=0ff1ba75-3c86-4baf-a6b1-1bb883839866&type=display
- Gong, Li., et. al. (2012). Metformin pathways: pharmacokinetics and pharmacodynamics. Accessed September 3, 2023. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651676/
- McCreight, L. J., et. al. (2016). Metformin and the gastrointestinal tract. Accessed September 3, 2023. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4742508/
- Molteni, L., et. al. 2024. Improving Type 2 Diabetes Care with Extended-Release Metformin: Real-Life Insights from a Physician Educational Program. Endocrine, metabolic & immune disorders drug targets, 24(12), 1422–1430. https://doi.org/10.2174/0118715303294909240221102552
- Subramaniam, K., et. al. (2021). A Common Drug Causing a Common Side Effect at an Uncommon Time: Metformin-Induced Chronic Diarrhea and Weight Loss After Years of Treatment. Accessed September 3, 2023. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8061542/
- Subramaniam, K., et. al. 2021. A Common Drug Causing a Common Side Effect at an Uncommon Time: Metformin-Induced Chronic Diarrhea and Weight Loss After Years of Treatment. Clinical diabetes : a publication of the American Diabetes Association, 39(2), 237–240. https://doi.org/10.2337/cd20-0101
- Tesvich, Marian PharmD; Mohundro, Brice L. PharmD. How should we manage metformin-induced diarrhea?. Evidence-Based Practice 16(6):p 8, June 2013. | DOI: 10.1097/01.EBP.0000540399.08855.8b
- Zhang, Qi. (2020). Effects of Metformin on the Gut Microbiota in Obesity and Type 2 Diabetes Mellitus. Accessed September 3, 2023. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7751595/
Read next
Can you take metformin without food?
If you take metformin without food you may end up with an upset stomach, especially if you are just starting treatment. Nausea and vomiting is one of the most common side effects with metformin and can occur in over a quarter of patients. Continue reading
Does metformin lower A1C, if so how much?
When metformin is used alone as monotherapy, it lowers A1C by about 1% to 2% on average. A1C is a measure of longer-term blood sugar control. In most patients, metformin is suggested as the initial treatment for type 2 diabetes, but its glucose-lowering effect may not be adequate for all patients if used alone. Continue reading
Does metformin cause weight loss?
Metformin, an oral type 2 diabetes medicine, may lead to a modest weight loss and does not usually lead to significant, if any, weight gain. In various clinical studies, when metformin was used alone, it led to a weight loss of 0.7 to 3.8 kg (1.5 to 8.4 lbs) in most patients, but other studies have shown weight loss up to 5.8 kg (12.8 lbs). Continue reading
See also:
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Drug information
- Metformin Information for Consumers
- Metformin prescribing info & package insert (for Health Professionals)
- Side Effects of Metformin (detailed)
- Metformin user reviews (658)
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