Open a PDF version to print this topic

HealthInfo Waitaha Canterbury

Medicines for constipation (adults)

Laxatives are medicines that help you to poo (pass a bowel motion). Different laxatives take different times to work – some work very quickly while others take a few days. Ideally, you should only use them for a short time. Changing what you eat and drink and becoming more active are the best longer-term treatments for constipation.

There are several groups of laxatives.

Bulk-forming laxatives

Bulk-forming laxatives are also called bulking agents or fibre supplements. This type of laxative is usually the first one that people try.

Bulk-forming laxatives work by making your poo softer, which makes it easier to pass. You can get them from your GP on prescription, or you can buy them over-the-counter at a pharmacy. You can also get some at the supermarket. Examples of bulk-forming laxatives include psyllium (Konsyl-D, Metamucil, Mucilax) and wheat dextrin (Benefiber).

Using bulk-forming laxatives

These can have some effect within 12 to 24 hours but it may take two to three days for bulk-forming laxatives to have their full effect.

It's important to drink plenty of fluid (at least eight cups a day) if you're taking a bulk-forming laxative as this helps to stop it blocking your digestive system.

While these laxatives help with constipation, some may cause bloating in your abdomen (tummy) or excess wind (farting). You can usually avoid this by starting on a small dose and gradually increasing it. Take them according to the manufacturer's directions or as your GP, pharmacist or dietitian tells you.

Stimulant laxatives

These stimulate the nerves in your bowel so it squeezes harder and pushes the poo (faeces) out. They are available as tablets or capsules that you swallow, or a suppository (a medicine that you put into your bottom).

The tablets or capsule usually take 6 to 12 hours to work but the suppository can work within 15 to 60 minutes.

Senna and bisacodyl are stimulant laxatives.

Osmotic laxatives

These work by drawing water from the rest of your body into your bowel to soften poo and make it easier to pass. Sometimes doctors prescribe an osmotic laxative for someone with faecal impaction.

Osmotic laxatives are available as a syrup or a powder to mix with water that you swallow, or a liquid or gel enema that you put into your bottom. The syrup and powders take one to three days to cause a bowel motion but enemas usually work within 30 minutes. Lactulose and macrogols are osmotic laxatives.

Faecal (stool) softener laxatives

These soften your poo. They are available as drops or tablets you swallow, or a liquid or gel enema that you put into your bottom, The drops or tablets can cause a bowel motion within 12 to 72 hours. Enemas usually cause a bowel motion within 30 minutes. Docusate is a faecal softener laxative.

Natural laxatives

Some foods, such as kiwifruit, prunes and linseeds, can help to relieve constipation for some people. Try one of the following at a time:


Just because you can buy some laxatives over the counter, doesn't mean they're safe for all people. If you have any bowel condition, are pregnant or breastfeeding, have diabetes or liver or kidney problems, it's important that you talk to your GP, practice nurse, or pharmacist before using any laxatives.

  HealthInfo recommends the following pages

Written by HealthInfo clinical advisers. Last reviewed July 2021.


Page reference: 49605

Review key: HICSA-13804