Cat Health Section – Constipation in Cats

What is Constipation?

Constipation is a difficulty in passing faeces, and the closely related term, obstipation means a complete inability to pass faeces.

What are the Symptoms of Constipation?

The main symptom is straining to pass faeces, with only small quantities of hard, dry faeces being passed. This must not be confused with cystitis, where the cat makes frequent visits to the litter tray, with the passage of small drops of urine, or possibly nothing at all. With constipation, the cat will usually make fewer visits to the litter tray than normal; cats with cystitis make more visits than normal. Cystitis can be an emergency, especially if the bladder is blocked. If in doubt bring her straight to the surgery.
Occasionally, cats will strain very hard to pass faeces, with the result being the passage of a small quantity of liquid faeces, which is mistaken for diarrhoea. In long standing cases, the cat will become depressed, go off her food, and may even vomit.

What is the Cause of Constipation?

There are a great many different possible causes of constipation, but they all act in the same way. Basically, something prevents the normal passage of faeces through the colon and rectum. As the main job of the colon is to remove water from the faeces, the retained material becomes progressively drier, and more difficult to pass. Thus, the faeces themselves form an obstruction, and add to the problem. Eventually, if the colon becomes distended enough, the muscles around the colon that propel the faeces forwards, will become overstretched and stop working, further compounding the problem.

If we consider what can prevent the smooth passage of faeces through the colon, we can see a few groups of diseases that can cause constipation:

Physical Obstruction.

  • Healed fractures of the pelvis.
  • Tumours.
  • Rectal stricture (narrowing of the anal opening).


  • Hair
  • Bones
  • Foreign bodies (e.g. plastic toys)

External Influences

  • Confinement with dirty litter tray.
  • Inability to stand such as occurs when more than one limb is fractured.


  • Inflamed anus, such as occurs with anal gland infection.
  • Fractures around the hind quarters.
  • Bite wounds.


  • Opiods (e.g. pethidine).
  • Kaolin (used to treat diarrhoea).

Nerve disorders

  • There are many of these, all fortunately very rare.

How is Constipation Investigated?

The single most common cause of constipation in cats is a healed pelvic fracture. When a cat is involved in a traffic accident, a fractured pelvis is a very common injury. Most of these heal uneventfully with rest alone. Unfortunately, in some cases, the healing process results in a severely narrowed pelvic canal, and recurrent constipation is the result. If this is the case, there will usually be a known history of pelvic fracture, and suspicion is immediately cast upon that as being the cause. Rectal examination (usually under anaesthesia), can confirm the diagnosis. However, there are some cats where this is not the case, and these present a much greater diagnostic challenge, and some or all of the following may need to be done:

X-ray. An x-ray will reveal any fractures of the pelvis, and whether or not they have healed. Some tumours within the colon or rectum may also be apparent on x-ray. This is not always the situation though, and if the pelvis is not itself involved in the disease process, x-rays are frequently normal.

Barium Enema. This is a variation in the x-ray technique. The colon is emptied of faeces, and barium (a liquid substance that prevents the passage of x-rays through it) is pumped into the colon. If there are any tumours or narrowings within the colon, they will usually be visible.

Colonoscopy. This technique involves the direct visualisation of the colon. There are two ways this can be achieved; both methods require the use of a general anaesthetic. The first is to use an endoscope (a bit like a flexible wire with a camera on the end) that is passed through the anus into the colon. A second way is with a cylindrical plastic tube inserted through the anus, and light shone down the tube. Whichever method is employed, localised areas of damaged or diseased colon can be inspected and biopsied if necessary. (A biopsy is a small piece of tissue that is removed from a part of the body). The biopsy is submitted to a pathologist for examination under the microscope.

How is Constipation Treated?

Initially, any medications that the cat is receiving that have the potential to cause constipation must be withdrawn completely.
After this, the first consideration when treating constipation, especially if recurrent, is to treat the underlying cause of the problem. However, even with a thorough work-up, the underlying cause may not always be apparent, in which case, symptomatic treatment only can be given.

Cats with constipation are often very dehydrated, and on initial presentation need to be given fluids intravenously for some time before the colon can be emptied. This treatment also has the effect of rehydrating the faeces, which makes them softer and easier to eliminate. Not all cats are in need of this every time though.

After rehydration, which usually takes about 24 hours, an attempt can be made to remove the faeces. Dietary modification can be used, but in most cases where veterinary help has to be provided, the cats have gone beyond the point where this will be of use. Therefore, the vast majority of cases will require an enema. This needs to be done under general anaesthesia in most cases. There are special enema solutions available that contain a variety of salts and citric acid. These have the effect of rehydrating the faeces by drawing water through the wall of the colon. One such product is called Micralax®. This works very well at stimulating defecation in normal cats, but in heavily constipated, or obstipated ones, it is much less reliable.

The technique mostly performed is the soapy water enema. The cat is anaesthetised, and warm, soapy water is gently pumped into the colon. This is massaged into the faeces which can then be removed. In some cats, it is not possible to remove all the faeces at the same time, and these may require an enema every day for several days. The colon can be damaged if it is handled too roughly, so it is better to do this than try in every case to remove all the faeces in one go.

All other treatments are aimed at preventing the recurrence of the constipation, and in the majority of cats, this involves modifying the diet in some way.

The most popular preventative treatment is the use of faecal bulking agents. These retain water within the faeces, making them softer, and easier to pass. Commonly used ones are bran, sterculia (Peridale®) and psyllium (plant extracts). Whichever product is used, a small amount (usually less than a teaspoonful) is mixed through the food. It is very important when taking these products that a plentiful supply of water is available. It is worth considering adding water to the food, or if your cat prefers it, to leave a tap dripping to drink from.
Laxatives can also be very useful, and again there are many to use. Commonly used laxatives are liquid paraffin, lactulose and Bisacodyl®. If these are overdosed, then diarrhoea is possible. There is the additional danger with liquid paraffin in that it is tasteless, and if administered manually (directly into the mouth), some of the liquid could pass into the lungs, and cause pneumonia. For this reason, liquid paraffin is best mixed through the food.

Drugs used to treat constipation
The drugs that are employed in the treatment of constipation act by increasing the force of the muscle contractions in the wall of the colon. It is very important when using these drugs to ensure that the colon is not actually blocked at the time of use, otherwise injury to the colon could occur.

Bethanecol (Myotonine®).Unlicensed for use in the cat, and there are frequently supply problems with this drug. It is occasionally successful in preventing the recurrence of constipation.

Surgery for Constipation
Where healed pelvic fractures are the cause, they can be treated by removing a part of the pelvis called the pubis. This is often quite successful at preventing recurrences, although the pelvis can try to heal across and the problem returns once more

Outlook for Affected Cats

In the vast majority of cases, affected cats lead full, normal lives. Despite this, in most cats, constipation is recurrent, susceptible individuals having repeated attacks all their lives. This is complicated by the fact that there is no “normal” number of times a day that a cat should pass faeces, and many affected cats never use an indoor litter tray. Consequently, many owners are completely unaware that their cat has a problem until it is totally obstipated.

Even with the closest supervision, most affected cats will suffer the occasional bout of constipation from time to time, especially where a healed pelvic fracture is the underlying cause.

There is the added danger that if an obstipated cat is not treated early enough, then the stretching of the muscles of the colon that results can lead to a condition called megacolon. With this, the colon becomes very distended, and flaccid, being almost incapable of moving faeces along. These cats may require surgery to remove the colon, which while not ideal because diarrhoea is quite common afterwards, does help to improve the cat’s quality of life.

If some cats, the irritation that develops around the anus can lead to ulceration and weakening of the anal sphincter muscle, which in turn can make the cat become incontinent. This is fortunately very rare.