7 Binding Cat Constipation Causes

What's behind that constipated cat, and how can you pass it?

See why your cat can't go. Via Torrey Wiley/Flickr


My 8-year-old female domestic shorthair cat, Beacon, is constipated. My vet recommended I add 1/8 of a teaspoon of over-the-counter Miralax in her wet food twice a day. She was defecating every two or three days, but it would always be loose.

Now my constipated cat hasn’t used the litterbox for a bowel movement in four days. My vet said to try a different, more potent laxative called lactulose. Tonight is the first night I’m trying it, but I’m wondering, where is this all leading? What causes my cat’s constipation? What might help to clear this up? I can’t afford a $2,000 endoscopy that my veterinarian mentioned. I am very frustrated. Why does my cat have to live on laxatives?


Every cat gets constipated once or twice over the course of his or her life. Recurrent constipation, however, is not normal.

Without examining your cat, I can’t say for certain the cause of your cat’s constipation, but there are many causes of cat constipation.

  • The most common cause of cat constipation is dietary. Diets low in fiber might predispose cats to constipation. Cats with limited access to water might have very firm stool.
  • Cats that swallow a lot of hair when grooming may also develop constipation.
  • Cats may retain feces and become constipated if their litterbox is dirty.
  • Some drugs can cause cat’s constipation.
  • Constipation can happen if the passage of feces is blocked, for example, by a tumor or stricture.
  • Cats may avoid defecation and become constipated if defecation is painful, for example, if cats have an anal sac abscess or a pelvic fracture.  
  • Certain metabolic, endocrine and neurologic disorders can also result in constipation

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Vets diagnose cat constipation by learning the cat’s defecation behavior and making a physical exam. On examination, most constipated cats have a large amount of feces that can be felt by the veterinarian. X-rays of the abdomen can confirm this and give information on the extent of the constipation. Your vet might request blood, urine and fecal tests to provide more information on the possible cause of the constipation. Endoscopy, which was recommended by your veterinarian, is unlikely to reveal the cause of your cat’s constipation, and is probably not warranted.

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If an underlying cause for the constipation can be identified it should be corrected if possible. You might need to change your cat’s diet. Your vet might prescribe laxatives or stool softeners. Miralax is usually my first choice in cats with occasional bouts of constipation. If Miralax isn’t controlling the constipation, I’ll often try lactulose next, so I agree with the way your vet handles this case. Unfortunately, you cat might need stool softeners for the remainder of her life.

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Keep the constipation under control, because chronic, recurrent bouts of constipation can eventually lead to megacolon, a condition of extreme, irreversible dilation of the colon. In cats with megacolon, the colon loses its ability to propel the feces, causing the feces to accumulate and cause an impaction. The prognosis for cats with megacolon is guarded.

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Discuss different types of cat foods and diets with your veterinarian. Your cat might get help from a highly digestible “low residue” diet, such as Hill’s Prescription i/d or Iams Low-Residue formula. Hydration helps control constipation. Feed your cat canned food rather than dry, and encourage your cat to drink lots of water. Putting water bowls in different places in your apartment, and getting a fountain-style water bowl might help. Good luck!

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Cats · Health and Care