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Constipation - Causes of constipation

Constipation usually occurs when stools remain in the colon (large intestine) for too long and the colon absorbs too much water from them, causing the stools to become hard and dry.

Most cases of constipation are not caused by a specific condition and it may be difficult to identify the exact cause. However, several factors can increase your chances of having constipation, including:

  • not eating enough fibre, such as fruit, vegetables and cereals
  • a change in your routine or lifestyle, such as a change in your eating habits
  • having limited privacy when using the toilet
  • ignoring the urge to pass stools
  • immobility or lack of exercise
  • not drinking enough fluids
  • having a high temperature (fever)
  • being underweight or overweight
  • anxiety or depression
  • psychiatric problems, such as those brought on by sexual abuse, violence or trauma


Sometimes, constipation may be a side effect of a medicine you are taking. Common types of medication that can cause constipation include:

  • aluminium antacids (medicine to treat indigestion)
  • antidepressants 
  • antiepileptics (medicine to treat epilepsy)
  • antipsychotics (medicine to treat schizophrenia and other mental health conditions)
  • calcium supplements
  • opiate painkillers, such as codeine and morphine
  • diuretics (water tablets)
  • iron supplements

If your constipation is caused by medication, the condition usually eases once you stop taking the medicine. However, you should not stop taking any prescribed medication unless your GP advises you to.

Speak to your GP if you experience constipation due to a medicine. They may be able to prescribe an alternative.


About two in every five women experience some constipation during their pregnancy, mostly during the early stages of their pregnancy.

Constipation occurs during pregnancy because your body produces more of the female hormone progesterone which acts as a muscle relaxant.

Your bowel normally moves stools and waste products along to the anus by a process known as peristalsis. This is when the muscles lining the bowel contract and relax in a rippling, wave-like motion. An increase in progesterone makes it more difficult for the bowel muscles to contract, making it harder to move waste products along.

If you are pregnant, there are ways that you can safely treat constipation without harming you or your baby. Read more about treating constipation.

Other conditions

In rare cases, constipation can be a sign of an underlying condition, such as:

Babies and children

Constipation in babies and children is quite common. It's estimated that up to one in every three children in the UK has constipation at any time. Poor diet, fear about using the toilet and poor toilet training can all be responsible.

Poor diet

Children who are over-fed are more likely to have constipation, as are those who do not get enough fluids. Babies who have too much milk are also more likely to get constipation. As with adults, it is very important that your child has enough fibre in their diet.

Toilet training

Make sure that you do not make your child feel stressed or pressured about using the toilet. It is also important to let your children try things by themselves (when appropriate). Constantly intervening when they are using the toilet may make them feel anxious and may contribute to constipation.

Toilet habits

Some children can feel stressed or anxious about using the toilet. They may have a phobia about using the toilet, or feel that they are unable to use the toilets at school.

This fear or phobia may be the result of your child experiencing pain when passing stools. This can lead to poor bowel habits, where children ignore the urge to pass stools and instead withhold them for fear of experiencing pain and discomfort. However, this will mean that their condition only worsens.

Other conditions

In rare cases, constipation in babies and children can be a sign of an underlying condition, such as:

  • Hirschsprung's disease – which affects the bowel, making it difficult to pass stools
  • anorectal malformation – where the baby's anus and rectum do not form properly
  • spinal cord abnormalities – including rare conditions such as spina bifida and cerebral palsy
  • cystic fibrosis – a genetic condition that causes the body to produce thick and sticky mucus, which can lead to constipation

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