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13-minute read

Key facts

  • Laxatives are medicines used to treat constipation, which is when you have trouble passing stools (poo).
  • The goal of all types of laxatives is to make it easier to pass bowel motions (poo).
  • You will not need to get a doctor’s prescription for most laxatives.
  • If you are considering taking laxatives, it’s a good idea to see your doctor or pharmacist for advice about what medicine to take and for how long.
  • To help prevent and treat constipation, make sure to eat a high fibre diet, drink lots of water and stay physically active.

What are laxatives?

Laxatives are medicines used to help prevent or treat constipation.

There are many different types of laxatives. Each type works in a different way, but the goal of all types of laxatives is to make it easier to pass bowel motions (poo).

For most laxatives, you will not need a doctor’s prescription. You can buy laxatives over the counter from a pharmacy. However, some types of laxatives may not be suitable for everyone. It’s important to check with your doctor or pharmacist before taking them.

What is constipation?

Constipation is when you have trouble passing stools (poo).

Symptoms of constipation include:

  • needing to strain to pass stools
  • passing lumpy or hard stools
  • feeling that your bowel isn’t completely empty when you finish passing stools
  • having fewer than 3 bowel movements per week

Many people suffer from constipation occasionally. It is more common in children, people who take strong pain medicines (such as opioids) and during pregnancy.

CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

How do laxatives work?

Different types of laxatives work differently.

  • Bulking agents work by adding fibre or ‘bulk’ to your stool. They also help ‘attract’ more water into your intestinal (gut) contents and increase its volume, making it easier to push the stool out.
  • Osmotic laxatives are substances that aren’t well absorbed by your gut. When they reach your intestines, they attract more water into your intestinal contents. This increases the volume of your stool and can make it easier and more comfortable to pass.
  • Stimulant laxatives stimulate the nerves in your gut so that the muscles contract more and the stool is pushed through your gastrointestinal tract more quickly.
  • Stool softeners and lubricants make your stool easier to pass by drawing more water and fats into your stool.

How do I take laxatives?

How you take laxatives will depend on the form they come in. The forms include:

  • oral liquids — given by mouth
  • dissolvable powders — given by mouth
  • tablets or capsules — given by mouth
  • suppositories — given rectally
  • enemas — given rectally

The table below has information about taking different types of laxatives.


Common medicines

How do I take it?

Time to take effect

Bulking agents
  • psyllium
Orally 24 hours
Osmotic laxatives
  • lactulose
  • sorbitol
  • macrogol 3350
  • sodium phosphate
Mostly orally but may also be given rectally

5 to 30 minutes for rectal preparation

1 hour to 2 days for different oral preparations

Stimulant laxatives
  • bisacodyl
  • senna
  • glycerol suppositories
Orally or rectally

15 to 60 minutes for rectal preparation

6 to 12 hours for oral preparations

Stool softener and lubricants
  • docusate

Orally or rectally

5 to 30 minutes for rectal preparation

2 to 3 days for oral preparation

How are laxatives used for bowel preparation (‘bowel prep’)?

Laxatives are routinely used to quickly clear the bowel of stool before procedures such as colonoscopy. This is known as bowel preparation or ‘bowel prep’.

There are different laxative formulations (oral or rectal) used for bowel prep. Your doctor will choose the formulation that is right for you and give you instructions on what you can eat or drink during this period. It’s important to carefully read and follow the instructions on the packet.

Bowel prep is usually taken the afternoon or evening before your procedure.

Taking bowel prep results in diarrhea, so make sure you have access to a toilet. Other common side effects include nausea, bloating or abdominal distension (swelling).

In some people, bowel prep can cause dehydration. If you feel dizzy or unwell while taking bowel prep, contact your doctor.

For more information about bowel prep, visit Bowel Cancer Australia.

What are the side effects of laxatives?

Side effects will vary depending on the type of laxative you are using.

Bulking agents — work in a similar way to high fibre foods in your diet. This means that they have few side effects and are usually safe to take long-term, but some people may experience bloating or flatulence (passing wind). 2 It is important to drink plenty of water when taking bulking agents for constipation.

Osmotic laxatives — when taken orally, these laxatives are relatively gentle but can cause bloating and increased wind.

Stimulant laxatives — can cause abdominal cramping. They should not be used in large quantities or for a long time as this may lead to dehydration. Long term use of stimulant laxatives is not recommended and can lead to worsening constipation.

Since many laxatives work by attracting more water into your stool, it’s important to make sure you drink enough water when taking medicines for constipation.

Some stool softeners and lubricants can reduce absorption of certain vitamins absorbed in your gut. Ask for your doctor or pharmacist for advice before using them long-term.

When should I see my doctor?

If you have constipation and are considering taking laxatives, it’s a good idea to see your doctor for advice. They can advise the best treatment strategy, including which medicine to take and for how long.

You should also see your doctor if the treatment they prescribe for your constipation hasn’t worked.

If you experience diarrhoea after using laxatives, stop the medicine. If your symptoms persist, see your doctor.

Some types of laxatives can increase your risk of dehydration. If you have symptoms of dehydration, stop the medicine and seek medical attention.

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

Are there any alternatives to laxatives?

There are many things you can do to help relieve constipation without, or in addition to, medicines:

Learn more about constipation and ways to treat it.

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Last reviewed: September 2023

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