What are laxatives?
Laxatives are a group of medicines that are used to treat constipation. They can be taken by mouth as liquids, tablets, or capsules, or they can be given via the rectum (back passage) – for example, suppositories, or enemas. Suppositories are pellet-shaped laxatives that are inserted into the rectum, via the anus. An enema is a liquid that is inserted into the rectum and lower colon, via the anus.
There are four main groups of laxatives that work in different ways. Each laxative often comes in various different brand names:
- Bulk-forming laxatives (also known as fibre supplements). For example, ispaghula husk, methylcellulose, sterculia. Unprocessed bran is a cheap fibre supplement.
- Osmotic laxatives. For example, lactulose, macrogols, phosphate enemas, and sodium citrate enemas.
- Stimulant laxatives. For example, bisacodyl, dantron, docusate sodium, glycerol, senna and sodium picosulfate.
- Faecal softeners. For example, docusate sodium, arachis (peanut) oil enemas, and liquid paraffin.
What is constipation?
Constipation is when faeces (stools or motions) become hard, and difficult or painful to pass. The time between toilet trips increases compared with your usual pattern. (Note: there is a large range of normal bowel habit. Some people normally go to the toilet to pass faeces 2-3 times per day. For others, 2-3 times per week is normal. It is a change from your usual pattern that may mean that you are constipated.) Sometimes crampy pains occur in the lower part of your abdomen. You may also feel bloated and feel sick if you have severe constipation.
Constipation may be caused by not eating enough fibre, or not drinking enough fluids. It can also be a side-effect of certain medicines, or related to an underlying medical condition. In many cases, the cause is not clear.
For more information see separate leaflet called ‘Constipation’‘.
How do laxatives work?
Bulk-forming laxatives are sometimes called fibre supplements. They increase the bulk of your faeces in a similar way to fibre. They partly work by absorbing water (a bit like blotting paper). The increase in the bulk of your faeces stimulates the muscles in your gut to squeeze faeces along and out of the body. Fibre is the part of plant food that is not digested. It stays in your gut and is passed in the stools (faeces). Fibre adds bulk to the stools.
Osmotic laxatives work by retaining fluid in the large bowel by osmosis (so less fluid is absorbed into the bloodstream from the large bowel).
Stimulant laxatives stimulate the nerves in the large bowel (the colon and rectum – sometimes also called the large intestine). This then causes the muscle in the wall of the large bowel to squeeze harder than usual. This pushes the faeces along and out.
Faecal softeners work by wetting and softening the faeces.
Which laxatives are usually prescribed or recommended?
Mostly, laxatives are taken by mouth (orally). In some cases, your doctor may prefer to treat your constipation by giving medication via the anus (back passage). But the choice of laxative usually depends on: what you would prefer, the symptoms of constipation that you have, how severe your constipation is, the possible side-effects of the laxative, your other medical conditions, and cost. As a general rule:
- Treatment with a bulk-forming laxative is usually tried first.
- If faeces 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 faeces are soft but you still find them difficult to pass then a stimulant laxative may be added in.
If you are pregnant or breast-feeding there are a number of laxatives that are thought to be safe to take. If you do need to take a laxative when you are pregnant or breast-feeding you should always ask your doctor or pharmacist for advice about which one you should use.
Sometimes, an enema is needed in severe constipation and can be used to clear out the lower bowel (rectum).
High doses of the macrogol osmotic laxatives are used to treat faecal loading and impaction (severe constipation) – this should be under the supervision and advice of a doctor.
Liquid paraffin used to be commonly used as a faecal softener. However, it is now not recommended, as it may cause side-effects such as seeping from the anus and irritating the skin, and it can interfere with the absorption of some vitamins from the gut.
How long do laxatives take to work?
Bulk-forming laxatives can have some effect within 12-24 hours but their full effect may take several days to develop.
Osmotic laxatives such as lactulose can take up to two days to have any effect so they are not suitable for the rapid relief of constipation. Macrogols act much faster, and can also be used in high doses to clear faecal loading or impaction.
Stimulant laxatives usually work within 8-12 hours. A bedtime dose is recommended so you are likely to feel the urge to go to the toilet sometime the following morning. However, you may try taking it at different times in the day to find the best time of day for you. Some people naturally have their bowel movements later in the day rather than in the morning.
Faecal softeners usually work within 24 to 48 hours.
Laxatives that are given via the rectum (suppositories or enemas) usually work within 15 to 30 minutes. Stronger osmotic laxatives (such as magnesium salts and phosphate enemas) can be used to clear the bowel quickly and in situations such as before bowel surgery.
How long should I take a laxative for?
This depends on what type of constipation you have. Most people only need to take a laxative for a short time, to get over a bout of constipation. Once the constipation eases, you can normally stop the laxative. Some people get into the habit of taking a laxative each day “to keep the bowels regular” or to prevent constipation. This is not advised, especially for laxatives which are not bulk-forming.
Some people have chronic (persistent) constipation and this can be more difficult to treat. So, in some situations, laxatives are needed for longer periods (sometimes even indefinitely) and they should not be stopped suddenly. Chronic constipation is sometimes complicated by a backlog of hard stools building up in the bowel (faecal loading) or even partially blocking it (impaction). If loading and impaction occur they need to be treated first, often with much higher doses of laxatives. Then a normal maintenance dose of laxatives is used to keep the bowels moving.
What are the side-effects?
It is not possible to list all the possible side-effects of each laxative in this leaflet. However, as with all medicines, there are a number of side-effects that have been reported with each of the different laxatives. If you want more information specific to your laxative then you should read the information leaflet that comes with the medicine.
Laxatives very rarely cause serious side-effects. Common side-effects include flatulence, cramps, diarrhoea, nausea, and bloating. Most of the side-effects can be avoided or reduced by starting off on a low dose and increasing the dose of oral laxatives gradually.
Bulk-forming laxatives – you may notice an increase in wind (flatulence) and abdominal bloating. This is normal and tends to settle down after a few weeks as the gut becomes used to the increase in fibre (or bulk-forming laxative). Occasionally, bulk-forming laxatives can make symptoms worse if you have very severe constipation. This is because they may cause abdominal bloating and discomfort without doing much to clear a lot of faeces which are stuck further down the gut. See a doctor if you feel that bulk-forming laxatives are making your symptoms worse.
These medicines sometimes react with other medicines that you may take. So, make sure your doctor knows of any other medicines that you are taking, including ones that you have bought rather than been prescribed. See the leaflet that comes with your particular brand for a full list of possible side-effects and cautions
When taking a laxative
Some important considerations are:
- Drinking plenty of fluid.
- Avoiding taking too much.
Drinking plenty of fluid
It is important that you drink plenty of fluid when taking any laxative. At least two litres per day (8-10 cups). 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. The faeces may become dry and difficult to pass.
Avoid taking too much
Taking too much of some laxatives can lead to diarrhoea and losing too much salt from the body. Taking too much of a bulk-forming laxative, or not drinking enough fluid with a bulk-forming laxative, causes a blockage in the gut rather than diarrhoea.
If you take bran, it is best to build up the amount gradually. Start with two teaspoons a day, and double the amount every five days until you reach about 1-3 tablespoons per day. You can sprinkle bran on breakfast cereals, or mix it with fruit juices, milk, stews, soups, crumbles, pastries, scones, etc.
Who cannot take laxatives?
In general, most people are able to take laxatives. You cannot take laxatives if you:
- Have a blockage in your gut.
- Have Crohn’s disease or ulcerative colitis, unless specifically advised by your doctor.
What about natural laxatives?
The information above is about laxatives that are commonly prescribed. However, it is well known that certain foods have laxative properties and some people prefer to try natural remedies. Foods that have laxative properties mainly work because they are high in fibre but some foods may also have some stimulant or osmotic properties. The following are two examples of natural laxatives.
Prunes (dried plums) have long been thought of as effective for constipation. However, up until recently, there had been little scientific proof of this. But, a research trial published in 2011 (cited at the end) lends support to the belief that prunes are good for treating constipation. In the trial, 40 adults with persistent constipation were studied as to the effect of prunes versus ispaghula (psyllium) – a commonly used treatment for constipation. Briefly, on average, 50 g of prunes (about six prunes) twice daily seemed to be better at easing constipation than 11 g ispaghula taken twice daily. This is just one small trial, but does seem to confirm many people’s belief that prunes are good for easing constipation.
The Beverley-Travis Natural Laxative Mixture
This recipe (detailed below) was studied in a research trial that involved older people in a care home. A treatment group was compared to a non-treatment group. The conclusion of the study stated that “the Beverley-Travis Natural Laxative Mixture, given at a dosage of 2 tablespoons twice daily, is easy to use, cost-effective, and more effective than daily prescribed laxatives at producing normal bowel movements”. So, it may be worth a try:
- Recipe ingredients – one cup each of: raisins; pitted prunes; figs; dates; currants; prune juice concentrate.
- Directions – combine contents together in a grinder or blender to a thickened consistency. Store in refrigerator between uses.
- Dose – two tablespoons twice a day. Increase or decrease the dose according to consistency and frequency of bowel movements.
How to use the Yellow Card Scheme
If you think you have had a side-effect to one of your medicines you can report this on the Yellow Card Scheme. You can do this online at the following web address: http://yellowcard.mhra.gov.uk
The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that your medicines may have caused. If you wish to report a side-effect you will need to provide basic information about:
- The side-effect.
- The name of the medicine which you think caused it.
- Information about the person who had the side-effect.
- Your contact details as the reporter of the side-effect.
It is helpful if you have your medication and/or the leaflet that came with it with you while you fill out the report.
References and Disclaimer | Provide feedback
- Constipation, Prodigy (January 2008)
- British National Formulary; 62nd Edition (Sep 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London (link to current BNF)
- Attaluri A, Donahoe R, Valestin J, et al; Randomised clinical trial: dried plums (prunes) vs. psyllium for constipation. Aliment Pharmacol Ther. 2011 Apr;33(7):822-8. doi: [abstract]
- Hale EM, Smith E, St James J, et al; Pilot study of the feasibility and effectiveness of a natural laxative mixture. Geriatr Nurs. 2007 Mar-Apr;28(2):104-11. [abstract]