Lactulose Side Effects in Cats

When giving your cat lactulose, you should be aware of all lactulose side effects that might occur.


Lactulose is a medication that is sometimes given to cats for constipation. It can also be used to help manage a hepatic encephalopathy disorder. While this medication is technically one for humans and not FDA approved for use in animals, it is very often prescribed to animals such as cats, dogs and birds. It is only available by prescription and is generally a very effective medication.

It is a sugar solution that is synthetically derived from lactose and forms a combination of fructose and galactose. It usually comes in the form of a syrup, but since cats often do not seem to care for the taste, it is also available in a powder form that can be mixed into the cat's food. 

Side Effects of Lactulose in Cats

There are a few side effects to this drug. 

  • Abdominal cramping. This is one of the more common side effects. It is something that should fade away with a little time. 
  • Flatulence. This is the other most common side effects of the medication. Like with cramping, it should go away after some time. 
  • Bloating. Another side effect that may occur in the beginning, but should go away with time.
  • Diarrhea. Particularly if your cat has an electrolyte imbalance, this is one you want to watch out for. This usually happens when your cat is given too much of the Lactulose or if your cat does not have enough water to drink while on the medication. This, of course, can lead to dehydration and is a more serious side-effect. Ensure your cat is not losing too much fluids or worse problems can arise.
  • Drooling. Since cats do not seem to care for the taste of the medicine, they sometimes begin to drool a lot in an attempt to try to get the taste out of their mouth. 
  • Allergic. As with any medication, it is possible that an allergic reaction may occur. If you suspect that your cat may have an allergy to Lactulose, stop administering the medication and contact your veterinarian.

As with all side-effects, if they are excessive or your cat seems to be feeling worse, contact your veterinarian right away to find out if the use of lactulose should be continued. 

What Other Concerns Are There?

Lactulose can interfere with the effectiveness of other medications that your cat may be taking. It is important to let your veterinarian know beforehand if your cat is taking anything so that this can be prevented. 

This medication can also cause an insulin imbalance in cats that have diabetes. Caution is recommended to make certain that the insulin levels remain steady while your cat is on this medicine.

Other things to keep in mind are that other laxatives should not be used with this product and that oral antacids can lower the level of Lactulose's effectiveness.