6 Metamucil Side Effects to Know About

Being constipated is an awful feeling. And it’s one that many people have experienced from time to time. Constipation is usually defined as having fewer than three bowel movements per week. It can also be passing stools that are hard or cause pain while you try to go. Constipation is very common and affects around 16% of U.S. adults.

Metamucil (psyllium husk) is commonly used to relieve constipation. It’s available over-the-counter (OTC). Metamucil is often recommended as a possible first-choice option for treating constipation. But this doesn’t mean it’s without risks or side effects.

Read on to learn about Metamucil side effects, including which side effects might warrant a call to a healthcare professional.

What is Metamucil?

Metamucil is an OTC laxative, known as a bulk-forming laxative. Its active ingredient is psyllium husk. Psyllium husk is plant-based and a natural fiber derived from the Plantago ovata plant.

Metamucil comes in several dosage forms, including capsules, wafers, and a powder you mix into a beverage. There are also many generic versions of Metamucil available that contain the same active ingredient.

Metamucil is mainly used for constipation or to help boost a person’s daily fiber intake. Healthcare professionals will also sometimes suggest using it to help treat diarrhea or lower cholesterol. Metamucil’s labeling states it can be used for adults and children ages 6 years and older.

How does it work for constipation?

Once Metamucil enters the body, it forms a gel-like substance in the stomach. It then travels to your intestines and acts as a source of soluble fiber. This helps your stool to absorb and retain more water. This makes your stool larger and softer, making it easier to go.

Metamucil doesn’t work right away. It takes about 12 to 72 hours to see its effects.

EXPERT PICKS: WHAT TO READ NEXT

• The right dose: Taking too much Metamucil can be one reason side effects happen. Read more about recommended Metamucil dosages and how to prepare your doses.

• Comparing options: Metamucil is one of several OTC constipation medications. Read more about how stool softeners compare to laxatives — and when one might be a better option.

• High-fiber foods: Metamucil isn’t the only way to increase your fiber intake. There are many high-fiber foods you can add to your diet, including raspberries, popcorn, and chickpeas.

Metamucil side effects at a glance

Metamucil and other bulk-forming laxatives are generally considered the safest type of laxatives to use. But this supplement still has some side effects to be aware of. Typically, these are mild for most people.

Common or mild Metamucil side effects include:

• Nausea or vomiting

• Gas

• Abdominal (stomach) cramping or bloating

• Diarrhea

• Constipation

Rare but serious Metamucil side effects include:

• Rectal bleeding

• Bowel obstruction (blockage in the intestines)

It’s also possible to have an allergic reaction to psyllium husk or any of the ingredients in Metamucil. Allergies can be mild, but they can also be life-threatening. Call 911 if you experience trouble breathing or swelling of the face, mouth, or tongue after taking Metamucil.

Below we’ll discuss six Metamucil side effects in more detail.

Good to know: As you’ll read below, drinking lots of water can help manage or prevent many Metamucil side effects. But if you need to limit your fluid intake, such as people living with heart failure, Metamucil may not be the best choice for you.

1. Nausea or vomiting

Nausea is a common side effect reported for many medications. And it can occur when using Metamucil, too.

If you feel nauseated after taking Metamucil, try drinking small amounts of clear liquids throughout the day. Eating smaller meals more frequently and avoiding spicy or fried foods can also help limit nausea.

Nausea from Metamucil is usually mild, but some people also experience vomiting. If vomiting happens, you should stop using Metamucil and contact a healthcare professional. There may be a better option to treat your constipation.

2. Gas

Feeling gassy can be uncomfortable and embarrassing. This side effect seems to be more common with Metamucil than with other bulk-forming laxatives. So if you feel gassy after starting Metamucil, trying a different medication in this class could help. There’s also OTC gas relief products you could try.

3. Abdominal cramping and bloating

Abdominal cramping and bloating are also common Metamucil side effects. Sometimes, they go hand-in-hand with feeling gassy. Bloating is common when you first start taking Metamucil, and it should go away after your body adjusts to it. You should start with smaller amounts and then gradually raise your dose.

Oftentimes, bloating happens when people don’t drink enough water when taking their dose of Metamucil. So be sure to take your doses with enough fluids. Following the directions on Metamucil’s OTC label can help manage and prevent bloating.

4. Diarrhea

Since Metamucil is a laxative, it can cause diarrhea or loose stools for some people. If this occurs, you should speak with a healthcare professional. Substances high in fiber can make diarrhea more uncomfortable while it’s happening. Your healthcare professional may recommend pausing or lowering your Metamucil dosage to help with diarrhea. You should also make sure to stay well hydrated until this side effect resolves.

5. Constipation

Even though Metamucil is used to treat constipation, it can actually make it worse in some cases. This Metamucil side effect can happen if you start with too high of a dose or don’t drink enough water while taking it. Staying well hydrated and preparing your doses as directed can help you avoid constipation while taking Metamucil. This means taking each dose of Metamucil with at least 8 oz of water.

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, such as a bowel obstruction.

6. Bowel obstruction

A bowel obstruction is a rare but serious Metamucil side effect. This can happen if you don’t follow proper instructions while preparing your doses. Metamucil needs water to work, so not drinking enough water with your dose 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 immediate medical care.

Does Metamucil cause weight loss?

It’s possible, but Metamucil is not a weight-loss medication. Some studies suggest that soluble fiber, such as psyllium (Metamucil’s active ingredient), can make you feel full longer. This may lead you to eat less calories overall during the day. And over time, this could cause some people to lose weight.

Taking Metamucil could be a low-risk way for many people to increase their daily fiber intake. But when possible, it’s better to add natural sources of fiber to your diet, such as fruits, vegetables, and whole grains. A healthcare professional can help you determine the best ways for you to get more fiber.

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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:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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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