Choosing a laxative
There are a wide range of laxatives that are available over the counter and they fall into 4 main categories.
1. Bulk forming laxatives (e.g. psyllium)
These can be used to supplement the fibre in your diet. Bulk forming laxatives absorb water in the bowel and increase the bulk of the stools and stimulate natural peristalsis. They need to be taken with adequate fluid to ensure that they work. They may cause gas and discomfort.
2. Osmotic laxatives (e.g. macrogol, lactulose)
Macrogol laxatives are often recommended by doctors as they are gentle and do not cause cramps or gas. They work by drawing water into the bowel and softening stools so they are easier to pass and generally produce a bowel movement in 1 to 3 days. They are also suitable for children.
3. Stimulant or irritant laxatives (e.g. senna, bisacodyl)
These work by stimulating nerves in the walls of the intestine, causing the muscles to contract and clear the bowel. They work quickly, often within hours but may cause cramps.
4. Lubricants and stool softeners (liquid paraffin, docusate)
These lubricate the walls of the bowel or moisten the stool so that stool can pass through more easily. They may take 1 to 3 days to be effective.
A review of clinical studies of laxatives1 published in the American Journal of Gastroenterology found that macrogol was the only over the counter laxative that was found to have good evidence to support its use in the treatment of constipation and was given a “Grade A Recommendation”. The review concluded that “there is minimal or weak evidence to support the use of many commonly used drugs for the treatment of constipation” (including the stimulant laxatives senna and bisacodyl and stool softeners).
1. American Journal of Gastroenterology 2005;100:936-971
