Constipation, or a difficulty in defecation due to hard stools, can be a very painful and embarrassing problem.
Some people are more prone to constipation than others, for a variety of reasons.
A lack of fibre or roughage in the diet.
Not going to the toilet when you need to - children are often guilty of this.
Blockage of the gut (which can be life-threatening).
A slow-moving bowel, as suffered by those with Irritable Bowel Syndrome.
Equally, many commonly-prescribed medications - including opiate pain relief such as morphine and codeine and some psychiatric medications, such as chlorpromazine (Thorazine) - can cause constipation as a side-effect, but most doctors have a pretty good working knowledge of the different types of laxatives.
If dietary treatments (which are the mainstay of therapy in most cases) don't work, and you're really blocked up, then some of the medications listed below can hopefully get things moving again. Bear in mind that the medications are not perfect - most laxatives can lead to some leakage from the bottom end for instance - and different types of laxatives are commonly used for different age groups.
Most laxatives are available over the counter in the UK.
They act on the bowel in one of four ways.
These substances are simply a supplement for dietary fibre, and work in the same way as any other fibre. The most well-known examples are Metamucil and Fybogel. Ideally, if your constipation isn't too serious, these agents should really be the first port of call before you get on the others.
Osmosis is the movement of water from a high concentration (of water) to a low concentration of water across a semipermeable membrane, such as the bowel wall. By increasing the concentration of large molecules on the inside of the bowel, you cause water to move from the bloodstream or surrounding tissues (where there are fewer particles dissolved in it, and therefore the water has a relatively high 'potential' to diffuse) into the bowel (where there are more molecules floating about, and therefore the water has a lower potential to diffuse, relative to the outside).
Some large molecules that will do the trick are non-digestible sugars such as lactulose1 that won't pass through the gut wall. Given orally as a thick, syrupy liquid, by drawing water in it softens up the stool and (hopefully) makes it easier to get rid of. The by-products of the laxative's metabolism can also, unfortunately, cause a degree of flatulence.
Other osmotic agents include large fatty molecules such as glycerine, which have the same basic action as lactulose, but are usually given from the bottom end as a suppository or enema2. Another tactic is using hypertonic3 saline as an enema.
Enemas are usually only given in high-care environments like hospitals and rest homes, because they can be hard on the elderly (and are virtually never used in children due to the unpleasantness of the method and the effectiveness of milder forms of laxatives).
These substances act on the surface of a hard stool and break down some of the surface tension, allowing water into the stool and softening it that way. One such example is docusate (Coloxyl). They work quite well in conjunction with osmotic agents.
These were probably the most commonly used laxatives historically (older generations may remember castor oil, for instance - variations of this are still being used today for treatment of kids with constipation). Some commonly used types today include senna (eg, Senokot) or danthron. These act to speed up the squeezing movements of the gut that push faeces along and, therefore, should never be used if bowel blockage is suspected. Long-term, they can irritate the bowel, causing discolouration and dysfunction of its action, so they should only be used for a short time. They are commonly combined with a stool softener into one tablet.
Some of these medications are available only on prescription, so if you are having continuing problems, and especially if you are having severe pain, make sure you consult your doctor.