Diarrhea is a common side effect of metformin, a medication prescribed for type 2 diabetes, PCOS, and other conditions that impact blood sugar levels.
You can stop metformin diarrhea by taking the medication with meals, lowering your dosage, or even temporarily taking an anti-diarrheal medication like Pepto-Bismol.
In almost every case, metformin diarrhea is a short-term side effect for people who have just started metformin. Late-onset metformin-induced diarrhea can also occur; it may be severe and even cause explosive diarrhea and/or incontinence.
As a woman with PCOS, I didn’t understand why the first treatment my doctor prescribed at the age of 18 felt like it was ruining my life. Nearing my wedding day, I found myself in the bathroom constantly, wondering how this would impact my first year of marriage.
Sure, managing my blood sugar and reproductive system should be worth it — but why did taking metformin give me chronic diarrhea?
I’m now 35 and have taken metformin 3 times for several months, every time with the same result. As I learned more about my condition, I also began to understand why metformin causes diarrhea for so many people (and how to offset this embarrassing side effect).
Let’s take a look at the causes of metformin diarrhea and what you can do about it.
This article may contain links to products. When you purchase anything using a link on this page, we get a small commission at no additional cost to you.
Why does metformin cause diarrhea?
First, metformin affects the levels of 2 chemicals, serotonin and GLP-1 (among others), in your intestines. This can speed up how quickly things move through your gastrointestinal tract (also known as increased gut motility), leading to diarrhea.
This drug (brand names Glucophage, Diabex, and Diaformin) also changes the way your body processes glucose, the sugar you get from food. This decrease in blood glucose levels can disrupt the balance of bacteria in your gut, which may cause diarrhea.
Lastly, metformin might make it harder for your body to absorb bile salts. These salts help you digest and absorb fats, and if they aren’t absorbed properly, diarrhea may occur.
Bile acid malabsorption from metformin may also cause your diarrhea to appear yellow.
It’s likely that all of these factors, rather than just one, play a role in causing diarrhea when you take metformin.
Less common factors that can also play a role in metformin diarrhea include celiac disease, hormonal conditions, and autonomic dysfunction.
Is metformin diarrhea common?
Yes, diarrhea is a pretty common side effect of metformin. 30% or more of the people who take this medication experience gastrointestinal side effects, including diarrhea.
Everyone’s body reacts differently to medications, so some people may have no GI side effects. For those who do, this chronic diarrhea usually gets better over time.
How long will metformin diarrhea last?
The duration of metformin-induced diarrhea varies from person to person. For many people, it’s just a temporary side effect that lasts around 2 weeks. Your body needs some time to adjust to the medication, and often, the diarrhea will go away on its own after this initial adjustment period.
However, some people may continue to experience diarrhea and other GI issues for a longer time.
If you’ve been dealing with diarrhea for more than 2 weeks, it’s a good idea to reach out to your doctor, as this can eventually lead to dehydration. They can offer guidance and suggest potential adjustments to your medication routine to help you manage this uncomfortable side effect.
How to stop metformin diarrhea
There are a few effective ways to stop diarrhea from diabetes medications like metformin:
- Give your body time to adjust: This diarrhea may be temporary and could go away on its own after a couple of weeks as your body gets used to the medication. If you can, give your body time.
- Take metformin with meals: Taking metformin with your biggest meal of the day can slow down the absorption of the drug, which may help reduce gut-related side effects like diarrhea.
- Switch to extended-release metformin: If you’re currently taking immediate-release metformin, ask your doctor about switching to the extended-release version. This formulation can help minimize gastrointestinal side effects.
- Adjust your dosage: Talk to your doctor about adjusting your metformin dose. A lower dose may help reduce diarrhea and other side effects. Your healthcare provider can help you decide if a lower dose will still manage your condition while reducing side effects.
- Take Pepto-Bismol: Pepto (bismuth salicylate) is an anti-diarrheal medication that can help slow gut motility. Especially in the first week or two of starting a new regimen or higher dose of metformin, take Pepto-Bismol to counteract gastrointestinal symptoms.
- Add dietary supplements: Consult your doctor about adding specific dietary supplements to your routine that might help alleviate metformin-induced diarrhea. If your metformin diarrhea is being caused by dysbiosis in the gut, probiotics may help.
- Change your medication: In cases where metformin and your body simply don’t get along, you can talk to your doctor about other FDA-approved alternatives. For diabetes drugs, these may include SGLT2 inhibitors (canagliflozin, brand name Invokana, or dapagliflozin, brand name Farxiga).
How to prevent getting diarrhea from metformin
To reduce your chances of experiencing diarrhea when starting metformin:
- Start with a low dose: Your doctor may initially prescribe a low dose of metformin to help minimize gastrointestinal side effects. In general, a starting dose of 500-850 mg per day may reduce your chances of uncomfortable side effects. Gradually increasing the dose over time may allow your body to adjust to the medication more smoothly.
- Take metformin with meals: Consuming metformin along with meals can slow down the drug’s absorption and decrease the likelihood of diarrhea. If you’re taking metformin once a day, take it with your largest meal, and if you’re taking it twice a day, take it with breakfast and dinner.
- Eat fewer eggs: While it’s unclear why this helps, eating 2 or fewer eggs per day while on metformin can help reduce your chances of developing metformin-related diarrhea.
- Choose extended-release metformin: Talk to your doctor about starting with the extended-release version of metformin. This formulation releases the drug more slowly, which can help prevent adverse side effects like diarrhea.
- Switch from tablets to capsules: One study found that changing metformin delivery from tablet to capsule form significantly decreased gastrointestinal side effects in patients taking metformin.
- Stay hydrated: Drinking plenty of water can help maintain your hydration levels, which is especially important if you’re experiencing diarrhea.
Other common side effects of metformin
Apart from diarrhea, metformin can cause various other common side effects. It’s essential to be aware of these potential side effects, as they can help you understand what to expect when taking the medication. Some other common side effects of metformin include:
- Bloating and gas: Metformin can sometimes cause bloating and gas (and related discomfort). This usually improves as your body adjusts to the medication.
- Stomach pain: Some people may experience stomach pain while taking metformin. Taking the medication with meals can help reduce this side effect.
- Nausea or vomiting: Metformin can cause nausea or vomiting in some people, but this typically subsides as your body gets used to the medication.
- Metallic taste in the mouth: A metallic taste is another common side effect of metformin. This can be annoying, but it often lessens over time.
- Heartburn: Metformin might cause heartburn. Taking the medication with food and avoiding lying down right after taking it can help alleviate this issue.
- Constipation: Although diarrhea is a more common side effect, some people may experience constipation while taking metformin. Drinking plenty of water and maintaining a high-fiber diet can help prevent constipation.
- Headache: Some people experience recurring headaches when they start taking metformin. It’s important to stay hydrated and consult your healthcare provider if the headaches become severe or persistent.
- Vitamin B12 deficiency: Taking metformin might interfere with your gut’s ability to absorb and metabolize vitamin B12, which is why 5-10% of people on metformin develop a deficiency. Symptoms of B12 deficiency are similar to anemia. This may or may not cause peripheral neuropathy caused by nerve damage. Your doctor will do a blood test if they suspect you’re deficient in B12, and this is typically corrected by intramuscular injections or oral supplements.
Keep in mind that most of these side effects are temporary and will likely improve as your body adjusts to the medication.
When to call your doctor
While diarrhea is a common side effect of metformin, in some cases, you should reach out to your healthcare provider for help. Contact your doctor if:
- The diarrhea is severe or persistent: If your diarrhea doesn’t improve after a couple of weeks, or if it’s accompanied by severe cramping or dehydration, it’s time to talk to your doctor.
- You experience additional side effects: Besides diarrhea, metformin can cause other gastrointestinal side effects like nausea, vomiting, or stomach pain. If these symptoms become severe or interfere with your daily life, consult with your healthcare provider.
- You have signs of lactic acidosis: Although rare, metformin can cause a serious condition called lactic acidosis, which requires immediate medical attention. Symptoms include muscle pain, difficulty breathing, dizziness, extreme fatigue, or feeling cold. If you experience any of these symptoms, contact your healthcare provider right away.
- Your weight changes dramatically: Metformin can actually support weight loss for people with PCOS, prediabetes, or diabetes. However, chronic diarrhea caused by metformin can sometimes lead to losing an excessive amount of weight from fluid loss, even after years on the medication. If you notice significant weight loss, talk to your prescriber to discuss whether or not what you’re experiencing is typical or a cause for concern.
- You notice symptoms of low blood sugar (hypoglycemia): Metformin can cause low blood sugar levels in some people. Symptoms of hypoglycemia include dizziness, confusion, sweating, and shaking. If you experience these symptoms, talk to your doctor as soon as possible.
It’s always a good idea to maintain open communication with your healthcare provider, especially when you’re starting a new medication.
Stopping metformin or making radical changes to a dietary or supplement regimen should only happen with expert input from your prescribing physician.