Bulk forming laxatives

Easy-to-read medicine information about bulk-forming laxatives – what they are, how to use them safely and possible side effects.

Type of medicine Also called
  • Bulk-forming laxatives
  • Fibre supplements
  • Psyllium husk
  • Ispaghula husk
  • Sterculia
  • Bonvit®
  • Konsyl-D®
  • Metamucil®
  • Mucilax regular®
  • Normacol®

What are bulk-forming laxatives?

  • Bulk-forming laxatives are used to treat constipation. Read more about constipation.
  • Bulk-forming are sometimes called fibre supplements.
  • Fibre is the part of plant food that is not digested and stays in your gut, and is passed in the stool. It  adds bulk to the stool (faeces).
  • Bulk-forming laxatives adds bulk to the stool (faeces) by absorbing water into the gut, making the stool softer and easier to pass.
  • Bulk-forming laxatives also swell or expand in the gut and activate the muscles in the gut to pass stools (faeces). 
  • Bulk-forming laxatives usually take 2 to 3 days to work. They are not helpful for the immediate relief of constipation. If you are unsure if bulk-forming laxatives are suitable for you, ask your doctor or pharmacist.    


  • The dose of the different bulk-forming laxatives will be different, depending on the product. 
  • Bulk-forming laxatives are available as capsules, granules or as a powder that you mix in water.
  • Examples of bulk-forming laxatives are:
    • Bonvit®
    • Konsyl-D®
    • Metamucil®
    • Mucilax®
    • Normacol®
  • Follow the directions on the label or the packaging. It will tell you how much to take, how often to take it, and any special instructions.

Special instructions

  • Drink plenty of fluids while you are taking a bulk-forming laxative – about 2 litres each day.
  • Not drinking enough fluid can cause blockage in the gut. 
  • Avoid taking other oral medication within 2 hours of taking a bulk-forming laxative.

Possible side effects

Like all medicines, bulk-forming laxatives can cause unwanted side effects, although not everyone gets them. Often unwanted side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Bloating
  • Gas in the stomach
  • Cramps
  • These are quite common when you first starting taking a bulk-forming laxative
  • This may settle in a few weeks
  • Tell your doctor if troublesome or gets worse
  • Allergic reaction including any skin rashes, itching, swelling of the face, lips, mouth
  • Tell your doctor immediately or ring HealthLine
Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr J Bycroft. Health Navigator NZ