How Do I Use Lactulose for Cats?

Cindy Quarters

Lactulose is a laxative medicine made from a combination of two sugars. Despite the fact that this medicine is labeled only for humans, using lactulose for cats is not uncommon. Cats are prone to a type of constipation called megacolon, in which the colon becomes impacted and enlarged. Dosing a cat with this condition is often an effective treatment. The frequency and size of the dose is based on the cat’s condition and size.

Lactulose may be used for cats that are unable to pass fecal matter.
Lactulose may be used for cats that are unable to pass fecal matter.

A cat that is suffering from megacolon will have a large amount of fecal matter in its colon. It is unable to pass some or all of the feces, resulting in the colon becoming stretched and enlarged as it fills with waste. Since lactulose is not absorbed in the small intestine but instead is passed intact to the large intestine, it is sometimes able to provide effective relief for this condition.

A lactulose prescription usually requires a trip to the veterinarian.
A lactulose prescription usually requires a trip to the veterinarian.

Another use of lactulose for cats is to treat hepatic encephalopathy. This condition is related to liver problems but actually affects the central nervous system. Cats with this condition may show a wide variety of symptoms such as seizures, blindness, change in urine output and color, and vomiting. When a cat with this condition is treated with lactulose, it shows a significant improvement in its overall health.

It is not unusual when using lactulose for cats that the affected animals will need to take this medication for the rest of their lives. Hepatic encephalopathy is caused by a physical deformity of the cat’s blood purification system. The symptoms can be treated but in most cases the cat cannot be cured. Ongoing use of this medicine helps to control the neurological symptoms of this condition, so it must be used daily.

Megacolon may require the ongoing use of lactulose for cats. Although not caused by any type of birth defect, once the colon has become stretched out, it does not function as well as it should. This can easily lead to recurring constipation. Regular treatment can prevent a recurrence of the problem, so it should be used on a daily basis at the lowest dose that provides relief.

There are some important considerations when using lactulose for cats. This medication can have serious, even fatal, consequences if the cat is diabetic, since it is essentially concentrated sugar. Cats that receive insulin will need to have it adjusted when taking lactulose to avoid diabetic complications. It is typically available only by prescription from a veterinarian, because it can have harmful side effects if not used properly. Not all animals can take lactulose and it must be used with caution to avoid serious consequences.

Cats on lactulose may need to take the medication for the rest of their lives.
Cats on lactulose may need to take the medication for the rest of their lives.

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Discussion Comments

@donasmrs -- 1m/day might be a better dose for a cat who just has constipation problems. Doses above 2ml/day are usually for cats who have constipation due to liver disease.

@donasmrs-- I think you should follow the vet's orders. If you think your cat will get side effects, then just break up the dose and give it to him throughout the day. For example, you can give him half the dose in the morning and half in the evening to help him adjust.

My cat has had to use lactulose in the past too and he tolerated it fairly well. 2.5ml/day is a typical dose for cats. My cat was on 2ml/day. Lactulose can cause diarrhea if given too much. If that happens, ask your vet about adjusting the dose.

By the way, did the vet say that your cat will have to be on this drug forever or just temporarily?


My cat has been having constipation frequently lately. He's had three vet visits because of it in the past one month. His vet has now put him on lactulose 2.5ml/day to treat his constipation.

I will start giving it to him today but is this a good dose to start with? My cat is very sensitive to drugs and usually gets all the side effects, so I'm wondering if he should start out with a lower dose.

Has anyone had experience with lactulose for cats?

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