6 Metamucil Side Effects to Know About

Metamucil (psyllium husk) is an over-the-counter (OTC) product that contains plant-based soluble fiber. People often take it as a daily fiber supplement for ongoing digestive regularity or other health benefits. You can also take Metamucil as needed for constipation relief. 

No matter why or how you’re taking Metamucil, it can cause side effects you should be aware of. Knowing what to expect can help you manage unwanted issues and know when to seek expert guidance.

Metamucil side effects at a glance

Below is a list of mild and and a list of rare but serious Metamucil side effects. Metamucil is generally well tolerated by most people, and you can likely manage most side effects on your own at home. But don’t hesitate to reach out for guidance if you experience any concerning side effects while taking Metamucil, even if they’re not listed below.

Mild Metamucil side effects include:

• Nausea or vomiting

• Gas

• Stomach cramps

• Bloating

• Diarrhea

• Constipation

Rare but serious Metamucil side effects include:

• Choking / esophageal blockage

• Rectal bleeding

• Bowel obstruction (blockage in the intestines)

It’s also possible to have an allergic reaction to Metamucil — especially if you accidentally inhale the powder before you mix it with liquid. Call 911 or seek emergency care if you have trouble breathing or swelling of the face, mouth, or tongue after taking Metamucil.

Let’s review six Metamucil side effects and how to manage them in more detail.

1. Nausea or vomiting

Nausea is a common Metamucil side effect. But it’s also a possible side effect of constipation. So nausea may improve as Metamucil starts working.

You should take Metamucil with at least 8 oz of liquid. Without enough fluid, Metamucil can form a lump in your stomach that can lead to nausea and vomiting. In severe cases, it may even block the esophagus and lead to choking. Staying hydrated helps Metamucil work and reduces the chance of nausea. It can also help prevent and treat constipation.

You can also help reduce the chance of nausea by starting with a low dosage of Metamucil and gradually increasing it as needed. This helps your body adjust to the additional fiber intake over time.

If at any point you experience severe nausea or vomiting along with stomach pain, seek medical care. This could be a sign of a bowel obstruction. (More on this later.)

2. Gas

Being gassy can feel uncomfortable and embarrassing. When you add fiber to your diet too quickly, it can create a large amount of soft stool that pushes against older, harder stool already in the bowel. This can stretch the bowel wall and cause gassiness, bloating, and discomfort. 

To reduce gassiness, it helps to start with a low dosage of Metamucil and increase it gradually. You can also try an OTC gas relief product, such as simethicone (Gas-X).

Metamucil seems to be more likely to cause gassiness than other bulk-forming laxatives. So if your symptoms don’t improve over time, talk to your healthcare team about trying a different type of fiber supplement or laxative.

3. Abdominal cramping and bloating

Abdominal cramping and bloating are also common Metamucil side effects. Sometimes, they go hand in hand with feeling gassy or constipated. So these symptoms often improve as your body adjusts and responds to Metamucil. Slowly raising your Metamucil dosage over time and mixing it with plenty of liquid can also help minimize these side effects.

If you have stomach pain and bloating that doesn’t improve or becomes severe, seek medical care. This could be a sign of a bowel obstruction.

4. Diarrhea

Since Metamucil is a laxative, it can cause diarrhea or loose stools for some people. If you experience diarrhea, it may help to reduce your Metamucil dosage or pause treatment until your bowels return to normal.

Be sure to drink plenty of fluids to avoid dehydration from diarrhea. If you have diarrhea that doesn’t resolve on its own or becomes severe, seek medical care for guidance.

5. Constipation

Even though Metamucil is used to treat constipation, it can actually make it worse in some cases. This Metamucil side effect is more likely if you start with too high of a dosage or don’t drink enough water while taking it.

If you have significant constipation, consider taking a fast-acting laxative to help clear out hard stool before starting Metamucil. This step can make the transition to taking Metamucil more comfortable. A healthcare professional can help select a laxative that’s safe for you.

Stop taking Metamucil and talk to your healthcare team if your constipation gets worse or lasts longer than 7 days. Severe constipation isn’t a typical Metamucil side effect and could indicate a more serious issue.

6. Bowel obstruction

Bowel obstruction is a rare but serious Metamucil side effect. This can happen if you don’t properly follow instructions while preparing your doses. As mentioned, Metamucil needs liquid in order to work properly. Not drinking enough fluids with your doses can lead to a blockage.

Symptoms of a bowel obstruction include being unable to pass stools, rectal bleeding, and severe stomach pain and vomiting. If you believe you have a bowel obstruction, seek emergency medical care.

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Written by:

Sarah Morin, RPh

Sarah Morin, RPh, has been a registered pharmacist for over 25 years. She started out as a hospital pharmacist, working at Rhode Island Hospital and then at the University of Connecticut Health Center.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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