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Causes of constipation

 The causes of constipation are either primary or secondary.

  • Primary causes include dietary factors, colonic motility (activity of movement), absorption of fluid in the colon, function of the anus and mechanism of evacuation, and behavioural and psychological factors.
  • Secondary causes include some types of medication, underactive thyroid, low calcium, diabetes, pregnancy, spinal cord injury, or conditions such as Parkinson’s disease and multiple sclerosis.

Diet and fluid

The relationship of fibre to constipation is actually rather complex. Some constipated people will respond very well to increasing the amount of fibre in their diets but others will not (see Change your diet). Similarly, increasing fluid in your diet does not always help constipation. Avoid dehydration, but bear in mind that increasing fluid intake may just make you urinate more rather than defecate more.

Irritable bowel syndrome

Irritable bowel syndrome can be a cause of constipation (known as IBS-C). See our section on irritable bowel syndrome (IBS) for more information.

Evacuation problems

Problems in the pelvic floor muscles can affect the evacuation of stools from the rectum. This is often termed obstructed defecation syndrome. For more information see rectocoele.

Behavioural and psychological factors

Persistently ignoring the need to defecate, what doctors call 'poor bowel habit', can exacerbate constipation. You might ignore the urge to open your bowels because you are too busy or because you dislike using a lavatory away from home or near other people (known as ‘shy bowel'). For more information see Toilet training and Shy bowel.

Stress or lifestyle changes can cause constipation. Depression can also bring about constipation. Nerves link the brain to the gut. Reduced activity of these nerves in depression affects the muscle activity of the bowel and results in constipation in some people.

Painful conditions

Pain from conditions such as an anal fissure can cause constipation.


Many medicines can cause constipation. Common culprits are: 

  • pain-killers or cough medicines containing codeine and ibuprofen
  • antacids (for indigestion) containing aluminium or calcium
  • iron tablets
  • some antidepressants (tricyclic and monoamine oxidase inhibitor types) and tranquillizers
  • some drugs for Parkinson’s disease and for epilepsy (Parkinson’s disease can itself cause constipation)
  • some diuretic drugs (for high blood pressure or heart failure)
  • drugs for high blood pressure (verapamil, nifedipine, atenolol, clonidine)
  • antihistamines (e.g. for hayfever)
  • antispasmodics (dicyclomine, mebeverine, peppermint oil)
  • calcium supplements (e.g. for osteoporosis).


About 1 in 3 pregnant women has constipation, probably because of the hormone progesterone. A simple laxative may help if constipation in pregnancy is causing problems, but you should speak to your doctor first.

Stopping smoking

Almost 1 in 10 quitters experience constipation for a while (Addiction 2003;98:1563–7).

Written by: Mr Andrew Ramwell
Edited by: Mr Andrew Ramwell
Last updated: Monday, May 12th 2014


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Comments on this article

Posted by Optional on 12/11/2012 at 07:04, United States

Every now and then I have very large and hard stools which leads to straining and hemorrhoids. Is it possible that the simvastatin could be causing this? I don't remember having such a problem before I started taking it several years ago.

Posted by bob on 04/05/2011 at 12:01, United Kingdom

I have been constipated for 5 years I have tried several diets, exercised an hour a day for months, lost two stone. gained two stone, I have tried every laxative available over the counter and perscribed to me for the last two years i have used micro enamas which does make a movement in my stools however it only eases the pain, they take an hour to do, when I go it is very noisey, this means I have to wait until no ones in and often means I dont like my partner staying with me for to long beause I wont go when his there. To say ive had enough is an understatement sometimes i think I would rather have everything below my rib cage amputated and be disabled as at frustrating as it may be i would be pain free, any advice?


View what people have said about constipation | Causes of constipation

Fascinating facts

An average person on a typical Western diet passes about 150 g (5 oz) of faeces each day. Faeces consist of about one-third solids and two-thirds water

The solid matter in faeces is cellulose from vegetables, dead cells cast off from the lining of the gut, bacteria, some salts and pigment from bile (which gives the brown colour)

Most of the waste matter from food is passed out in the faeces within 72 hours, but in healthy people up to 30% may remain in the colon for a week or more

Defecation is a very efficient process, normally taking only 10 seconds. Presumably it has to be quick - animals (and primitive man) cannot run from a predator easily if they are in the middle of defecating. This is probably why it is even quicker when we are frightened

In the USA, more than $800 million is spent on laxatives each year

Constipation results in more than 2–5 million visits to doctors in the USA each year

About 4,500,000 people in the USA say they are constipated most or all of the time (National Health Interview Survey)

In a UK survey, 6% of people said they had suffered from constipation in the past year, 13% had some difficulty in passing their faeces at least once a month, and 19% took laxatives at some time

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