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Metamucil: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on July 15, 2022.

1. How it works

  • Metamucil is a brand (trade) name for a powdered form of psyllium husk, which is a type of soluble fiber derived from the seed husks of Plantago ovata, a type of plant. Metamucil may be given to relieve constipation or to lower cholesterol.
  • The active ingredient in Metamucil, psyllium husk, absorbs and holds water, which causes it to swell and add bulk and moisture to hardened stools, allowing them to slide though the colon easily. This relieves constipation. Metamucil lowers cholesterol by trapping bile acid in the gut, which instead of being reabsorbed, is removed in the body's waste.
  • Metamucil belongs to the class of medicines known as laxatives. It may also be called a fiber, a bulk-forming laxative, or ispaghula. Psyllium may also be called Plantago seed, plantain seed, psyllium husk, or psyllium hydrophilic mucilloid.

2. Upsides

  • May help relieve occasional constipation.
  • Can improve bowel irregularity.
  • Has cholesterol-lowering properties particularly when given in addition to a diet low in cholesterol and saturated fat and may be used to reduce the risk of coronary heart disease.
  • May be used as a dietary fiber supplement.
  • May be used for other, unapproved, indications, such as reducing blood sugar levels and HbA1c levels in people with, or at risk for, type 2 diabetes, and to help manage irritable bowel syndrome.
  • Available as granules, powder, wafers, and capsules.
  • Many different brands of psyllium fiber are available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Common side effects include abdominal cramps, bloating, and changes in stool consistency. May aggravate hemorrhoids or anal fissures.
  • If the daily recommended amount of fluid is not drunk, then Metamucil could cause severe constipation, especially in people who are already dehydrated.
  • Some products may contain sugar, sodium, or phenylalanine (phenylketonurics should avoid). People on a low-salt diet or with uncontrolled high blood pressure may need to check with their doctor before using.
  • May not be suitable for people with nausea, vomiting, abdominal pain, rectal bleeding, phenylketonuria, or difficulty swallowing.
  • Contraindicated in people with fecal impaction or gastrointestinal obstruction (bowel blockage).
  • Some people are allergic to psyllium, and Metamucil should be stopped and emergency treatment sought if hives, difficulty breathing, or facial swelling occurs.
  • Not suitable for children younger than six.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Metamucil is a fiber supplement that may be used to treat constipation, improve stool consistency, and lower cholesterol. When used to treat constipation, adequate daily fluid intake is vital to ensure its effectiveness.

5. Tips

  • A good way of adding fiber to your diet, but should be taken in addition to a healthy, mainly vegetable-based diet, together with exercise, and weight control. Take with a full glass of water.
  • If you are taking Metamucil as a way to help lower your cholesterol, avoid eating foods that are high in fat or cholesterol.
  • If you are taking Metamucil for irritable bowel syndrome, mix the powder with food (preferably yogurt). Less fluid may need to be drunk daily if you are using it for this indication.
  • Make sure you take Metamucil with a full glass of water, otherwise it can swell in your throat and cause choking. Ensure you drink at least six glasses of fluid each day while taking Metamucil.
  • Swallow Metamucil capsules whole one at a time.
  • May be taken with or without food.
  • Mix Metamucil powder with at least 8 ounces of water or fruit juice before drinking straight away. Do not swallow the dry powder. Avoid breathing in the powder when mixing as this may cause a runny nose, watery eyes, and wheezing.
  • Call your doctor immediately if you start bleeding from your rectum, develop severe stomach pain, experience bloating after taking Metamucil, or have any other worrying side effects.
  • Do not take Metamucil for more than seven days in a row without a doctor's advice. Laxatives can be habit-forming if they are taken too much or for too long. If you find Metamucil is not working for you, call your doctor for advice. Also, call your doctor if your symptoms worsen or do not improve.
  • Talk to your doctor or pharmacist before taking if you have had a sudden change in bowel habits in the past two weeks or if you are pregnant or breastfeeding.
  • Do not give Metamucil to children younger than six years unless on a doctor's advice.
  • Keep your Metamucil in a cool, dry, place, away from moisture and heat.

6. Response and effectiveness

  • A bowel movement can be expected within 12 to 72 hours of taking Metamucil.

7. Interactions

There are few significant interactions with Metamucil. Medications that may interact with Metamucil include:

  • lactulose
  • the radiopharmaceutical, fludeoxyglucose (18F).

Metamucil may also affect the absorption of other medications and some vitamins and minerals, as a result of medication being detained in the fiber mass in the intestines and then excreted. Taking medications or vitamins and minerals at least two hours before or two hours after Metamucil can prevent this from happening.

Note that this list is not all-inclusive and includes only common medications that may interact with folic acid. You should refer to the prescribing information for folic acid for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Metamucil only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2022 Revision date: July 15, 2022.