Lactulose for Cats - Uses, Dosage and Side Effects

Laura García Ortiz
By Laura García Ortiz, Veterinarian specialized in feline medicine. Updated: May 30, 2024
Lactulose for Cats - Uses, Dosage and Side Effects

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Lactulose is a type of laxative which can be used in both human and veterinary medicine. As a laxative, it is used to counteract the retention of stool or slow intestinal transit, i.e. constipation. Constipation itself has many causes, but it can be exacerbated if it affects the dilation of the large intestine and results in megacolon. Lactulose is mainly used as an oral solution, sold under various brands names such as Duphalac®, Cephulac®, Constulose®, Enulose® and Generlac®. If lactulose is not administered, the cat can suffer serious problems related to constipation such as pain, dehydration, anorexia and other life-threatening issues.

At AnimalWised, we help you to understand the uses, dosage and possible side effects of lactulose for cats. We should also point out prolonged constipation requires veterinary consultation.

  1. What is lactulose for cats?
  2. Can I give lactulose to my cat?
  3. Lactulose for cats uses
  4. Dosage of lactulose in cats
  5. Contraindications of lactulose in cats
  6. Lactulose for cats side effects

What is lactulose for cats?

Lactulose is a non-absorbable sugar which has a laxative effect on a cat's digestive system. The purpose of laxatives is to increase bowel movements by loosening stools. Lactulose is made up of galactose/glucose units derived from milk, although it is not present in raw milk. It is a disaccharide that cannot be hydrolyzed by intestinal enzymes in mammals, but it is metabolized by colonic bacteria.

When metabolized, lactulose forms CO 2 and low molecular weight acids such as formic, lactic and acetic acid. These products increase osmotic pressure, which mobilizes water towards the intestine. This results in a laxative effect and acidifies the content of the colon. In turn, this produces migration of ammonia from the blood towards the colon, where it is retained as ammonium ion, expels with the stool, increases peristalsis and softens the stool.

Lactulose also has uses for hepatic encephalopathy. This is a neurological condition which results from liver failure. When lactulose for cats is used it is due to hyperammonemia, i.e. high levels of ammonia in the blood. Lactulose helps to bind ammonia in the colon, preventing it from diffusing it back into the blood. Signs of liver dysfunction vary[1], so lactulose will only be used after diagnose by a veterinarian.

Learn more about why your feline is constipated in our article on why a cat hasn't pooped in four days.

Can I give lactulose to my cat?

There are various brand names for lactulose which are designed for human use, Cephulac® being one of the most common in the USA. Duphalac® is a common brand in other territories. However, you should ensure you choose a version which is suitable for veterinary usage. In this case, it should be specific for use in cats. Other brand names for veterinary lactulose include Generlac®, Constulose®, Enulose ®and Kristalose®.

Although lactulose is an over-the-counter medication for humans, it is usually only available in veterinary use with prescription. You should always consult your veterinarian if thinking of using lactulose or any laxative for cats.

Lactulose for cats uses

Lactulose in cats is used to treat acute or chronic constipation or megacolon in cats. This is because it facilitates the exit of feces from the colon, a problem which can result from the following causes:

  • Stress (changes in the home, moving, introducing new animals or people, loud noises, etc.)
  • Rectal or perianal pain
  • Stenosis or obstructions of the colon due to fractures, rickets, neoplasms, perineal hernia or spinal injuries (cauda equina syndrome)
  • Idiopathic megacolon resulting in hypomotility and accumulation of feces in the colon that causes severe constipation
  • Neurological damage such as alteration of the hypogastric or pelvic nerve due to dysautonomia, trauma or neuromuscular alteration due to trauma in the sacro-coccygeal region
  • Congenital megacolon due to diseases from birth such as aganglionosis, anorectal agenesis or absence of the caudal and sacral spinal segment in tailless breeds such as the Manx cat

As detailed above, lactulose is also used to treat hyperammonemia which can lead to hepatic encephalitis. This is a result of liver disease, something you can learn about in our article on liver failure in cats.

Dosage of lactulose in cats

The dose for cats is 400 mg lactulose per kg body weight per day. This corresponds to 0.6 ml of the product per kg body weight of the cat once daily. However, administration should preferably be divided into two or three daily doses. It can be mixed with food or given directly in the cat's mouth via syringe. Lactulose begins to take effect two or three days after commencement of treatment.

Care must be taken when administering the medication and it must be kept away from children. Accidental ingestion can cause diarrhea and flatulence. As it contains benzyl alcohol, it can produce hypersensitivity reactions or allergies to this preservative.

Contraindications of lactulose in cats

Lactulose should not be used in cats in the following cases:

  • Cats with total gastrointestinal obstruction
  • Cats with digestive perforation or risk of suffering it
  • Cats with hypersensitivity to the active substance or to the excipient
  • Diabetic cats
  • Cats with previous hydroelectrolytic imbalances due to the risk of producing diarrhea

The drug is safe in pregnant and lactating cats. It should not be mixed with other veterinary drugs unless expressly stipulated by a veterinarian.

Lactulose for cats side effects

In cats, oral absorption of lactulose by the small intestine is less than 2%. This means it is not metabolized and is excreted essentially unchanged in the urine within 24 hours of ingestion.

Some side effects this medication can produce in cats are the following:

  • Gas and flatulence
  • Stomach dilation
  • Colic
  • Anorexia
  • Lethargy
  • Loss of appetite
  • Diarrhea
  • Dehydration

In case of observing any of these adverse effects, it is important to go to the clinic to report it. The specialist will decide what to do and may prescribe a different laxative. We will also need to check their stools in case there is a possible intestinal blockage in the cat.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Lactulose for Cats - Uses, Dosage and Side Effects, we recommend you visit our Medicine category.


1. Salgado, M., & Cortes, Y. (2013). Hepatic Encephalopathy: Diagnosis and Treatment. Compendium: continuing education for veterinarians (E1-E10). Yardley, PA : Veterinary Learning Systems.

  • Spanish Agency for Medicines and Health Products. Technical sheet of Laxatract 667 mg/ml syrup for dogs and cats. Retrieved from:
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Lactulose for Cats - Uses, Dosage and Side Effects