Why Does Metformin Cause Diarrhea?

Metformin is a first-choice drug in the treatment of type 2 diabetes and belongs to the class of drugs known as Biguanides. Diabetes causes an increased blood sugar level and metformin acts to reduce blood sugar levels.

However, metformin is known to cause diarrhea in many people. This side-effect is mostly noted shortly after commencing the medication and gets better with time in many cases.

Why Does Metformin Cause Diarrhea?

Even though there are a number of proposed hypotheses, the exact manner in which metformin causes gastrointestinal problems is not very certain. On one hand, it is believed that gastrointestinal problems likely result from the concentration of metformin in the intestine after been taken by mouth.


On the other hand, it is believed that metformin structurally can fit into a certain receptor in the body called 5-HT3. When the 5-HT3 receptor is activated, effects like nausea, vomiting and diarrhea result.

Dealing with Metformin-Induced Diarrhea

Having to deal with diarrhea as a side effect of metformin use can be very uncomfortable. It can sometimes lead to poor compliance thereby affecting the goal of therapy. Here are a few tips that can help you deal with this side effect.

1. Be Informed

The first step in dealing with Metformin-induced diarrhea is to understand that it is caused by the drug you are taking. If unsure, speak with your doctor or your pharmacist about the medications you are currently using and the effects that you have been experiencing. Your Physician is in the best position to advise you. It is better to take metformin alongside your meals. It helps control this side effect.

2. Oral Rehydration

In treating any form of diarrhea, oral rehydration is important. In order to prevent dehydration, you need to drink a lot of water to replace the fluids that your body has lost.

Oral rehydration solution (ORS) is recommended for use as a fluid replacement therapy because it contains some other nutrients that your body would have lost due to frequent watery stools.


3. Dose Reduction

Your doctor may recommend a gradual reduction in the dose of the metformin you are currently using. This also helps to reduce the intensity of the diarrhea side effect.

4. Controlled-Release Metformin

Switching to a controlled released version of the medication is another way to manage this side effect. A controlled release medication releases small amounts of the medication at scheduled intervals over a period of 24 hours.

Hence, per time, only little amounts enough to keep a steady concentration is available in the body and subsequently, the side effect is greatly reduced.

5. Switching Medication

Sometimes, no matter what is done to get rid of this side effect, the desired results might not be achieved. Your doctor may decide to change the course of therapy to an alternative anti-diabetic medication that would not cause this side effect.

6. Monitoring your Diet

You may be able to manage recurring diarrhea or the frequency by paying attention to your diet. Eating smaller meals frequently, switching to low carbohydrate meals, can help manage the frequency of diarrhea.


Foods and drinks with high potassium content are recommended. Examples include bananas, potatoes, diluted fruit juices that are free from sugar.


Metformin-induced diarrhea can be very uncomfortable, especially because the medication is essential in managing diabetes. While the above measures can help in dealing with the situation, it is important to consult your doctor. Your doctor is certified to inform and counsel you on the most suitable management for you.

Latest posts by Raliat Ola-Dauda, PharmD (see all)
  • Save
Share via
Copy link