Constipation is a term used to describe absent, infrequent or difficult passage of faeces (stools).

When constipation occurs, faeces are retained longer than normal in the colon or rectum (large bowel), and as a result the faeces tends to become dryer and harder (through absorption of water across the intestine), which may make the problem worse.

Animals with constipation may exhibit signs of pain when trying to pass faeces (defecate), and this may be accompanied by excessive straining to pass faeces. If there is prolonged constipation, the faeces may become severely impacted in the colon and rectum, and this is known as obstipation. With repeated bouts of constipation or obstipation the colon can become distended and lose its ability to contract and push faeces towards the rectum, a condition called megacolon (meaning very enlarged colon).


Causes of constipation

Many different factors can cause or contribute to constipation in cats. Some of the important causes and considerations are listed here:

Behaviour and lifestyle

Cats can be reluctant to defecate if, for example:

  • A litter tray is dirty
  • There is competition (with other cats) for a litter tray
  • The cat doesn’t like the type of cat litter used
  • The litter tray is in a noisy or unpleasant place
  • The cat has had a bad experience when using a litter tray


Older cats especially may suffer from pain and discomfort associated with, for example, osteoarthritis. This may make getting in and out of the litter tray or adopting a position to defecate painful.

In some cases there may be pain from the colon or rectum if there are abnormalities there or if the cat has eaten something that causes trauma to the lining of the colon as it passes through. Abscesses or other painful skin conditions around the anus may also cause reluctance to defecate.


Water is absorbed from faeces in the colon and if cats are dehydrated (or not drinking enough) they will try to reabsorb more fluid from the colon, resulting in dry and hard faeces. Chronic kidney disease is common in older cats and leads to increased urine production and so cats tend to become mildly dehydrated and this can be a cause of constipation.

Metabolic disorders

Some metabolic disorders such as low concentrations of thyroid hormones (hypothyroidism, a rare condition in cats), and low blood potassium or calcium can interfere with the ability of the colon to contract and can thus predispose to constipation.

Neurological problems

The nerves that control the contraction of the bowel can be damaged as a result of trauma (eg, road traffic accidents and ’tail-pull’ injuries affecting the lower spine). In some cases, faecal incontinence (uncontrolled defecation) may arise, but in others, faecal retention and constipation are seen (sometimes with urinary retention – inability to pass urine – also).

Obstruction of the colon

Deformities of the pelvis (for example a healed fracture of the pelvis after trauma) can cause narrowing of the pelvic canal. This can cause compression of the colon in the pelvis and a build up of faeces behind the area of constriction. If severe, and if this results in prolonged obstipation, secondary megacolon (see below) may develop. Narrowing of the colon can also occur through strictures, tumours, foreign bodies etc.

Idiopathic megacolon

Megacolon can result from several months of severe constipation and obstipation, causing a gradual and permanent deterioration in the ability of the colon to contract due to persistent over distension. However, megacolon can also arise in the cat as a primary disease with no obvious underlying cause – this is termed idiopathic megacolon. In this disease a problem develops with the muscle of the wall of the colon itself, leading to a progressive inability to contract.


Signs of constipation

Signs of constipation in the cat are usually easy to spot, and include:

  • Straining and difficulty passing faeces (called tenesmus)
  • Pain when passing faeces
  • Decreased frequency of defecation
  • Production of small, hard dry faeces (stools)

There may be increased visits to the litter tray with non-productive straining, however it can sometimes be difficult to decide whether the cat is straining to urinate or defecate.

Occasionally, especially in cases of obstipation, the cat may pass faecal fluid rather than formed faeces during straining, which looks like diarrhoea. This can happen because the retained faecal matter irritates the lining of the colon and stimulates some fluid secretion. In severe cases, cats may also lose their appetite and may vomit.


Diagnosis and investigation

Because of the various things that may cause or contribute to constipation, your vet may have to do a number of investigations as well as examining your cat and talking with you about what has been going on. This will be especially important in cases of recurrent or severe constipation. Investigations may include:

  • Blood and urine tests
  • X-rays or ultrasound
  • Endoscopy – using a medical ’camera’ to look at the inside of the colon and perhaps get biopsies (a procedure called colonoscopy)
  • Careful examination under sedation or anaesthesia



The treatment for constipation in any individual cat will depend on the underlying cause of the problem, its severity and its duration. In severe constipation or obstipation, cats may initially have to be hospitalised and placed on intravenous fluids, and then faeces may have to be removed from the colon under anaesthesia. This can be a long process in severely obstipated cats, and sometimes more than one anaesthetic may be required to remove all impacted faeces.

Several options may be used for the ongoing management of cats with constipation:

  • Maintaining good hydration – keeping a good fluid intake will be helpful in managing constipated cats, so in general feeding wet (tins, sachets) rather than dry food may help, and encouraging the cat to drink as much as possible.
  • Litter tray management – is also important, reviewing the site, size, number and type of litter trays to encourage your cat to use them as frequently as possible. See how to choose and use a litter tray for your cat.
  • Dietary management – diet change can be very helpful in cases of constipation. Using a diet with a high moisture content helps (see above) but also with mild cases of constipation having a high fibre diet (or adding fibre to the diet) may help the regular passage of softer faeces. Your vet will be able to advise you on a good diet or dietary supplement. In cats with severe constipation (for example with megacolon), sometimes a very low residue diet (along with laxative drugs, see below) may actually work better than a high fibre diet, and your vet may also suggest trying this.
  • Enemas – enemas may sometimes be helpful to relieve mild constipation
  • Laxative drugs – A wide variety of different laxative drugs are available, although many may not be specifically licensed for use in cats. Many of these can be very helpful in managing cats with recurrent constipation. Laxatives tend to fall into a few different categories:
    • Lubricant laxatives – these are designed to lubricate the colon and make passage of faeces easier. Examples include liquid paraffin. Generally these are not recommended in cats, they are not safe for long-term use and can cause severe problems should the cat inhale the liquid paraffin rather than swallowing it.
    • Emollient laxatives – these are drugs that are designed to promote water retention in faeces and thus make the faeces softer. They have a mild action but can sometimes be useful alone or in combination with other drugs
    • Osmotic laxatives – these act by drawing water into the faeces to make it softer, and can have a potent action. One of the most commonly used osmotic laxatives is a non-absorbed sugar called lactulose. This can be administered to cats as a liquid (or mixed in with food) and the dose can be adjusted to effect. The actualise is not absorbed from the intestine but its presence in the faeces draws in and retains water. This can be used alone or in combination with other laxatives.
    • Stimulant laxatives – some drugs stimulate the contraction of the muscle in the wall of the colon to help propel faeces towards the anus. These drugs act in different ways and some are only safe for short-term use.
  • Prokinetic drugs – these are similar to stimulant laxatives in that they assist the neuromuscular control of contractions in the colon. A common example of a drug that has been used widely in cats is cisapride (although this has more limited availability now). This can be used long-term, and can be helpful when combined with other control measures (e.g., lactulose and a low residue diet)
  • Surgery – if medical management is not successful in managing constipation, surgery (to remove most of the colon – an operation known as subtotal colectomy) and may be performed. Although this is quite major surgery, and cats will inevitably have diarrhoea for a period of time afterwards, the long-term results of this type of surgery are often very good. In general, cats quickly adapt and the diarrhoea begins to resolve quite quickly.


Chronic constipation is a relatively frequent problem especially in older cats. Although milder cases can often be successfully managed with medical and dietary treatment, some cats, and particularly those more severely affected, may eventually need surgery.