Medications used to treat constipation

Treatment with a laxative is needed only if self care measures, such as eating plenty of fibre and drinking enough fluid, do not work well in relieving constipation.

What are the different types of laxatives?

There are several types of laxatives that differ in how quickly they start working, how helpful they are in different situations, possible side effects, their taste and their cost.

The four main groups of laxatives are:

More-detailed information about these four types of laxatives, including common brand names, is provided in the table at the bottom of this page.

How are laxatives taken?

There are different forms of laxatives. Some can be taken by mouth; others as an enema inserted in the bottom:

  • Tablets, capsules and powders are taken by mouth (called oral formulations), and depending on the type of laxative, can take hours or days to work.
  • Rectal formulations (enemas or suppositories) are inserted into the rectum (bottom). These are usually effective within minutes to an hour, and are mainly used as a last resort to treat severe constipation.

Which laxative should I use?

Always seek guidance from your doctor or pharmacist as to which laxative is best for you. 

Usually, treatment with a bulk-forming laxative is tried first. If faeces (poos) remain hard despite using a bulk-forming laxative then an osmotic laxative tends to be tried, or used in addition to a bulk-forming laxative.

If bowel movements are soft but you still find them difficult to pass then a stimulant laxative may be added in. In cases of severe constipation (impaction), high doses of the osmotic laxatives may be used.

How to use laxatives safely

  • Drink plenty of water:
    • When taking laxatives, you should try to drink at least 8 to 10 cups of water a day.
    • This is because laxatives, especially an osmotic laxative, can make you dehydrated.
    • If you take a bulk-forming laxative and you do not drink enough fluid this can cause a blockage in the gut as the faeces (poos) may become dry and difficult to pass.
  • Use only for short periods of time:
    • Long-term use can make your body dependent on them, so your bowel no longer functions normally without them. 
    • Generally, it is recommended that you do not take laxatives for more than 5 to 7 days in a row.
    • If symptoms persist after this time contact your doctor for advice.

Possible side effects

Like all medicines, laxatives can cause side effects, although not everybody gets them. The common side effects of laxatives are:

  • stomach pain or cramps
  • bloating, gas in the tummy
  • flatulence or 'farting'.

More-detailed information on laxative types 

Bulking agents (fibre supplements) Examples
  • Bulk-forming laxatives adds bulk to the faeces (stools, poos) by absorbing water into the gut, making the bowel movement softer and easier to pass. 
  • They usually take 2 to 3 days to cause a bowel movement.
  • unprocessed bran
  • psyllium (Konsyl D®, Mucilax®, Metamucil®)
  • ispaghula (Isogel®)
Stimulant laxatives Examples
  • Stimulant laxatives act on the bowel's nervous system to get the bowel moving.
  • The tablets or capsules usually cause a bowel movement after 8 to 12 hours. A bedtime dose is recommended, so you are likely to feel the urge to go to the toilet sometime the following morning. 
  • The rectal formulations (suppositories or enemas) are quick acting and cause a bowel movement after 15 minutes but may take up to 1 hour.  
  • Tablets
    • bisacodyl (Dulcolax tablet)
    • sennoside B (Senokot tablet)
  •  Suppositories
    • bisacodyl (Dulcolax suppository, Lax-Suppositories®)
    • gylcerol suppositories
Osmotic laxatives Examples
  • Osmotic laxatives use water to soften the bowel motion, by drawing water into the bowel. The bowels become filled (distended) with extra fluid, and this stimulates the muscles of the walls of the bowels to contract. These muscle contractions squeeze the bowel movement along.
  • The oral formulations usually take 1 to 3 days to cause a bowel motion.
  • The rectal formulations (enema) usually cause a bowel motion within 30 minutes.
  • Syrup or liquid 
    • lactulose (Laevolac)
    • Movicol. 
  • Enema
    • Fleet enema
    • Micolette enema
    • Microlax enema.
Faecal or stool softeners Examples
  • These laxatives soften the faeces (stool,poo).
  • The oral formulation usually cause a bowel movement after 12 to 72 hours.
  • The rectal formulations (enema) usually cause a bowel motion within 30 minutes.
  • Tablets and drops
    • docusate (Laxofast capsule, Coloxyl tablet)
    • Coloxyl drops.
  • Enema
    • docusate (Coloxyl enema)

Learn more

New Zealand Formulary Patient Information


Laxatives New Zealand Formulary

Credits: Sandra Ponen, Pharmacist. Last reviewed: 15 Mar 2016