Written by Sonia Amin Thomas, PharmD, BCOP | Reviewed by Joshua Murdock, PharmD, BCBBS Published on May 6, 2022
Key takeaways:
- Metamucil (psyllium husk) is an over-the-counter supplement used most commonly for constipation. But it has other benefits and is a good source of fiber.
- Common Metamucil side effects include gas, bloating, and nausea. It’s best to take Metamucil as directed to help prevent potentially dangerous side effects, such as blockages in the intestines.
- Speak with your healthcare provider before adding Metamucil to your daily routine. They can help make sure it’s a good fit for you.
GoodRx Health
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). And since Metamucil actually refers to a line of products, many versions of it are available. It’s 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 provider.
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 providers 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.
5 Metamucil side effects you should know about
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. Below are five potential Metamucil side effects:
1. Nausea or vomiting
Nausea is a common side effect reported for many medications. And it can occur when using Metamucil, too. This is usually mild, but some people also experience vomiting. If vomiting happens, you should stop using Metamucil and contact your healthcare provider. 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. Oftentimes, bloating happens when people don’t drink enough water when taking their dose of Metamucil.
In most cases, bloating is temporary and goes away after your body adjusts to it.
4. Diarrhea
Since Metamucil is a laxative, it can cause diarrhea or loose stools for some people. If this occurs, you should stop taking it. You should also make sure to stay well hydrated until this side effect resolves.
5. Bowel obstruction
A bowel obstruction (blockage) is a serious side effect that can occur with Metamucil. This is especially true if you don’t follow proper instructions while using it. Metamucil needs water to work, so not drinking enough water with your dose can lead to a blockage. Symptoms of a bowel obstruction include severe stomach pain, nausea, and vomiting. If this happens, a healthcare provider should be contacted immediately.
What can I do to manage the Metamucil side effects?
Drinking plenty of water with Metamucil can help limit or prevent some of the side effects, like bloating. This is important for every form of Metamucil, not just the powder that you drink. So if you have fluid restrictions, like with heart failure, Metamucil may not be the best choice for you.
Carefully following dose directions on Metamucil’s packaging will also help manage and prevent side effects. It’s best to start with smaller amounts and then raise the dose slowly.
For example, adults using Metamucil powder packets should start by dissolving one packet in 8 ounces (about 240 mL) of water once a day. They can then slowly raise this dose to one packet 3 times a day as needed.
When should I contact my healthcare provider about Metamucil side effects?
As mentioned above, if you have symptoms of a bowel obstruction, contact your healthcare provider right away. Blockages require medical care. Nausea, vomiting, or abdominal cramps that don’t go away after stopping Metamucil warrant a call to your healthcare provider as well.
It’s 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.
You should also seek immediate medical care if you experience any rectal bleeding while taking Metamucil. Rectal bleeding could be a sign of a more serious problem.
Some signs of rectal bleeding include:
- Bright red blood in your stool
- Dark red blood in your stool
- Black stool
- Blood on toilet paper upon wiping
- Blood in the toilet water after using the bathroom
Remember, Metamucil can take a few days to start working. But it shouldn’t take more than that. If you have constipation that lasts longer than 7 days, it’s time to reach out to your healthcare provider for additional guidance on what to do.
The bottom line
Metamucil is a bulk-forming laxative that’s readily available OTC. It’s mainly used to help relieve constipation. Metamucil side effects, such as gas and bloating, are typically mild for most people.
It’s very important to follow the directions on the packaging to help prevent serious side effects. Although considered safe for most people, it’s always best to speak to your healthcare provider before taking Metamucil to make sure it’s right for you.
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