Miralax for Cats: Is it Safe?

Constipation is a common and uncomfortable problem for humans, as 20 percent of the general population experience this issue [1]. Miralax is a laxative medication readily available and used to treat constipation in humans. This medication has also become popular in treating constipation in our feline friends. 

In this article, we will explain what Miralax is, whether or not it is safe to use in cats, what conditions it treats, how to administer it to cats, its common side effects, and dosing information. 

What is Miralax? 

Miralax is an osmotic laxative, which means it draws water into the intestines to soften stools, stimulating bowel movements and easing constipation. The active ingredient in Miralax is polyethylene glycol 3350, or PEG 3350. In 1999, the FDA approved Miralax for use in humans to treat occasional constipation. The product was approved for over-the-counter use in 2006 [2]. 

Most recommended forms of this medication are available to pet parents without a prescription from their local pharmacy. Formulations of PEG 3350 that contain added electrolytes are only available with a prescription. The version of Miralax that is used for cats is the same as the human product.  

Is Miralax Safe for Cats?

Miralax is generally considered a safe medication to give to cats. However, it is always best to confirm with your veterinarian that it is okay to give Miralax to your cat. Miralax should not be given to cats that are dehydrated, as it can lead to further dehydration and electrolyte abnormalities. 

Cats suspected of having gastrointestinal obstruction, gastric retention, bowel perforation, toxic colitis, or ileus should also not be given Miralax. PEG 3350 solutions containing electrolytes (eg, CoLyte®, GoLytely®) should be used with caution in cats with inflammatory bowel disease.

What is Miralax Used For in Cats? 

Miralax is most commonly used to relieve and treat constipation in cats. Prescription PEG 3350 containing electrolytes is mostly used to clean out the bowels before endoscopy procedures and to help flush toxins out of the gastrointestinal tract for cats that have eaten something harmful. There are no other currently recommended uses for Miralax in cats. 

In humans, Miralax has recently been found to be more effective than lactulose for treating hepatic encephalopathy (a nervous system disorder brought on by liver disease). Miralax may be useful to treat this condition in cats, but studies are lacking [3]. 

How to Give Miralax to Cats

Miralax comes in a powdered form meant to be dissolved in liquid. However, it is okay to give the powder to cats as long as it is mixed with food, preferably canned or wet food. The powder is tasteless and odorless, so most cats will take Miralax without a fuss. 

When Miralax is used to treat severe constipation or in preparation for an endoscopy procedure, it is generally administered as a liquid solution. It must be given by a trained veterinary professional. 

Miralax Side Effects in Cats

To date, there is only one published study that evaluated the use and safety of Miralax in six cats over 4 weeks. For this reason, side effects are not well known. In the published study, most cats tolerated the medication without side effects, but one cat developed sporadic vomiting [4]. 

Besides vomiting, nausea and cramping are possible side effects of giving cats Miralax. 

It is thought that long-term use of Miralax may cause dehydration, low sodium levels, and/or high potassium levels. Since Miralax pulls water from the body and into the stools, it can make cats dehydrated. It is recommended to feed wet or canned food to cats taking Miralax to help prevent dehydration.

Since Miralax speeds up how quickly things move through the intestines, other drugs and medications should not be given at the same time as Miralax. Other oral medications should be given at least one hour before Miralax administration. 

Miralax should not be given with other laxatives or stool softeners. Miralax should be used with caution with other medications that may cause electrolyte abnormalities and dehydration, such as diuretics and ACE inhibitors. 

Miralax Dosage for Cats

For cats, the recommended dose is generally ⅛ to ¼ teaspoon of powder mixed in with food twice daily. Your veterinarian will be able to give you more specific instructions based on your cat’s condition and needs. 

Make sure to speak with your veterinarian before giving your cat Miralax. The best treatment for constipation is to try to determine the underlying cause, which generally requires lab tests and X-rays at a minimum.

Do not give the labeled over-the-counter Miralax dose to cats as this is the dose for humans and is much too large for cats. 

Alternatives to Miralax

While many cat parents appreciate the convenience and efficacy of Miralax, this over-the-counter laxative designed for humans isn’t the only option for cats.

Lactulose is a prescription oral solution that can be used as a laxative and stool softener in cats. Though it works similarly to Miralax, its active ingredients are different. It can be compounded in cat-friendly flavors. And it is also available under the brand name Kristalose.

Vetasyl is a non-prescription fiber supplement that comes in capsule form. Like Miralax, it can be sprinkled over your cat’s food. It’s made with psyllium husks to provide gentle, effective relief from constipation. You should discuss supplements with your veterinarian before adding them to your cat’s dietary routine.

And if hairballs are contributing to your cat’s constipation, you might opt for a product specifically designed to move them along, such as Cat Lax or Laxatone. These non-prescription gels come in tasty flavors, so you just apply them to your cat’s nose or paws for them to lick off. When used daily, the gel lubricates hairballs, allowing them to move through the digestive tract more easily.