If you are one of the millions of people with diabetes who rely on metformin to manage your blood sugar levels, you may have experienced an unwelcome side effect: diarrhea. While metformin is an effective medication for controlling diabetes, its association with gastrointestinal issues, especially diarrhea, is well-documented. In this article, we will explore why does metformin cause diarrhea and what you can do to manage this common side effect.

Understanding Metformin

Metformin, a widely prescribed medication for type 2 diabetes, belongs to a class of drugs called biguanides. It works by lowering blood sugar levels primarily by decreasing the amount of glucose produced by the liver and increasing the sensitivity of muscle cells to insulin. Metformin is usually taken orally and is often the first-line treatment for type 2 diabetes because of its efficacy and relatively low risk of causing low blood sugar (hypoglycemia), a common concern with other diabetes medications.

Why Does Metformin Cause Diarrhea?

The exact mechanism behind metformin-induced diarrhea is not fully understood, but several theories have been proposed:

  1. Gastrointestinal Disturbance: Metformin is thought to affect the gastrointestinal tract directly, leading to various gastrointestinal symptoms, including diarrhea. It may irritate the lining of the stomach and intestines, causing an increase in bowel movements.
  2. Altered Gut Microbiota: Some research suggests that metformin can alter the composition of the gut microbiota. Changes in the gut microbiome can impact digestion and lead to gastrointestinal symptoms, including diarrhea.
  3. Increased Water Content: Metformin may increase the water content in the intestines, which can soften stools and lead to diarrhea.
  4. Dose-Dependent Effect: The likelihood of experiencing diarrhea with metformin may be dose-dependent, meaning higher doses are more likely to cause this side effect. Your healthcare provider will usually start you on a lower dose and gradually increase it to minimize gastrointestinal issues.

Managing Metformin-Induced Diarrhea

Experiencing diarrhea while taking metformin can be uncomfortable and inconvenient, but there are steps you can take to manage this side effect:

  1. Adjust the Dosage: If diarrhea is severe or persistent, speak to your healthcare provider about adjusting your metformin dosage. Lowering the dose may help reduce gastrointestinal symptoms while still effectively managing your blood sugar levels.
  2. Timing Matters: Taking metformin with meals or right after a meal can sometimes help mitigate diarrhea. Food can help slow down the absorption of the medication and reduce the irritation to the gastrointestinal tract.
  3. Stay Hydrated: Diarrhea can lead to dehydration, so be sure to drink plenty of fluids to stay hydrated. Water, clear broths, and oral rehydration solutions can be helpful.
  4. Fiber-Rich Diet: Consuming a diet rich in soluble fiber can help bulk up stools and alleviate diarrhea. Foods like oats, apples, and bananas are good options.
  5. Probiotics: Some individuals have found relief from metformin-induced diarrhea by taking probiotic supplements. Probiotics can help restore a healthy balance of gut bacteria.
  6. Over-the-Counter Remedies: Over-the-counter anti-diarrheal medications like loperamide (Imodium) can be used to temporarily relieve diarrhea, but it’s essential to consult with your healthcare provider before using them regularly.
  7. Patience and Communication: It’s crucial to communicate openly with your healthcare provider about any side effects you experience. They can offer guidance and alternative treatments if necessary.


While metformin is a valuable medication for managing diabetes, it does come with the potential side effect of diarrhea. Understanding why metformin can cause diarrhea and implementing strategies to manage this side effect can help improve your overall experience with the medication. Remember that managing diabetes is a collaborative effort between you and your healthcare provider, so be sure to discuss any concerns or side effects you encounter during your treatment journey. In some cases, alternative medications may be considered if metformin-induced diarrhea remains a significant issue. By taking a proactive approach to managing this side effect, you can continue to effectively control your blood sugar levels and enjoy a better quality of life.