Laxatives | Cancer Research UK
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What laxatives are for

Laxatives are used to help relieve constipation. Before taking any laxative you need to be sure that you really are constipated. Normal bowel movements vary from person to person. So, if you have cancer, you should always check with your doctor or nurse before taking any type of laxative.

If you have a bag on your tummy to collect your poo (stools or faeces) it is called a colostomy or ileostomy. You may not be able to take some types of laxatives. Your doctor or nurse will want to assess your constipation and the cause of your constipation before recommending the best treatment for you.

Remember that if you have constipation and vomiting, do not take laxatives without checking with your doctor or nurse first. If your bowel is blocked, the laxatives will do more harm than good.


Types of laxatives

You can buy many laxatives over the counter at the chemist, supermarket, or health food store without a prescription from your doctor or nurse. Other type of laxatives need a doctor’s prescription. Laxatives come as

  • Tablets, capsules or granules
  • Foods, such as bran
  • Syrups
  • Powders that can be made into a drink by adding water or fruit juice
  • An enema that you have into the back passage
  • Suppositories that you have into the back passage

Jodrell lab CRI tablets

There are several types of laxatives, including

Bulk forming laxatives

These work by swelling up inside your bowel. This helps to soften and increase the amount of stool, which encourages your bowels to move and push the stools out. This type of laxative can take a few days to work properly. Examples include

  • Wheat bran
  • Fybogel
  • Celevac
  • Normacol

Stimulant laxatives

Stimulant laxatives work by speeding up bowel movement. They can take between 8 and 12 hours to work. Examples include

  • Bisacodyl
  • Docusate sodium
  • Glycerol suppositiories
  • Senna (Senakot)
  • Syrup of figs
  • Co-danthrusate (Normax) and co-danthramer

Osmotic laxatives

Osmotic laxatives work by drawing more water into your bowel. This makes your stools softer and easier to pass.

Examples of these osmotic laxatives include

  • Lactulose syrup
  • Macrogols (Movicol and Idrolax)
  • Magnesium salts (Andrews liver salts, Epsom salts, Cream of magnesia)
  • Phosphate enemas
  • Sodium citrate (Microlette and Microlax enemas)

Opioid receptor blockers

People having opioid type painkillers often have constipation. A drug called methylnatrexone (Relistor) can help to reduce constipation in people having opioid painkillers when other laxatives have not worked.


Side effects of laxatives

Different laxatives have different side effects. Bulk forming laxatives can cause wind and swelling in the abdomen. They can also block up your bowel. To prevent this you need to drink plenty of water.


Other types of laxatives can cause stomach cramps and wind, and large doses can cause diarrhoea. The side effects usually go away once your bowels have opened. But if you continue to have cramping or abdominal swelling, or if you develop diarrhoea, let your doctor or nurse know straight away.


Taking herbal supplements for constipation

Some herbal medicines claim to be laxatives that can help relieve constipation. Some are safe and do work. But we don’t know exactly how some of these medicines will react with your particular cancer drugs. 

Herbal products aren't necessarily all safe. Although they are natural products and you can buy them over the counter at a health shop, some may be harmful to take alongside cancer treatment. So it is very important to let your doctor know if you are planning on taking any herbal medicine alongside your cancer treatment.

There is detailed information about herbal medicine in the complementary therapy section.

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Updated: 21 May 2014