Miralax for Cats: Safe Dosage, Uses, and Side Effects

Almost every condition humans experience has a feline equivalent. This is true of constipation, a common problem especially in senior cats. It can also occur in dehydrated cats or cats with chronic medical conditions. 

There are various treatments for constipation in cats. One of the most frequently recommended is MiraLAX. MiraLAX is a gentle osmotic laxative that draws water into the colon and is used for people and animals. It can help your cat have regular, comfortable bowel movements, and it’s safe. This guide explains what MiraLAX is, the correct dosage, potential side effects, and alternatives to it.

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What is MiraLAX?

MiraLAX is the brand name for polyethylene glycol. It’s an osmotic laxative, which draws water into the colon. This softens hardened stool, making it easier for a cat to pass.

Here are some important facts about MiraLAX.

• It’s odorless and tasteless. This is particularly convenient for cats, who can be challenging to medicate if they sense medication in their food. You can mix MiraLAX into their wet food, and cats will not suspect it’s there.

• Some laxatives, called stimulant laxatives, cause contractions to help move stool along. This is a harsher method for treating a cat’s constipation. MiraLAX does not do that. 

• MiraLAX is off-label in veterinary medicine, but veterinarians commonly use it. It is sold over the counter to the public.

• MiraLAX does not cure constipation in cats, but treats it and can be used long-term.

Uses of MiraLAX in cats

There are several reasons cats become constipated. 

1. Mild or moderate constipation: Dehydration, stress, or low-fiber diets can cause short-term constipation. 

2. Chronic constipation: Constipation may not be short-term. Recurring constipation can occur secondarily to arthritis, obesity, or low water intake. In those instances, cats can be given MiraLAX daily or on a near-daily basis.

3. Megacolon management: Megacolon is a condition in which the large intestine (colon) becomes stretched and enlarged, losing its ability to contract, leading to chronic constipation. Cats need stool softening agents long-term for this. MiraLAX can be very beneficial to cats with this condition, although some cases may be severe enough to require surgery or additional medications.

4. Post-anesthesia constipation: Some cats, after they’ve had a procedure involving anesthesia, can become temporarily constipated. MiraLAX can help in those cases.

Related article

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Here’s how to deal with cat constipation.

Common dosage of MiraLAX in cats

The recommended dose of MiraLAX for an average adult cat is one-eighth to one-fourth of a teaspoon, once or twice daily. It can be mixed into their wet food, and cats generally accept it because it doesn’t taste bad.

Here are some general guidelines for giving MiraLAX to a cat.

• Start on the low side, using one-eighth of a teaspoon once daily.

• Adjust as needed. You can increase the dosage to one-fourth of a teaspoon and to twice daily if the stool remains hard.

• Mixing with food is essential, so you must feed MiraLAX with moist food.

• Hydration is also crucial. Make sure your cat always has access to plenty of water.

• Cats with chronic constipation or megacolon may need even higher dosages or more frequent dosages, but do not change the dosage on your own. Consult your veterinarian.

After starting MiraLAX, most cats will have a bowel movement within 24 to 72 hours. If you don’t see improvement after three days, get in touch with your veterinarian.

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Potential side effects of MiraLAX

Even though MiraLAX is safe most of the time, as with anything else, it could have side effects. This can occur especially if you administer the wrong dose or if your cat is dehydrated.

Common side effects:

• Increased thirst

• Mild abdominal cramping

• Diarrhea

• Gas

Other side effects, which can be of more concern: 

• Lethargy

• Electrolyte imbalances

• Dehydration

• Vomiting

If your cat has diarrhea for more than 24 hours, becomes more lethargic, or shows signs of dehydration (reduced appetite, sunken eyes, dry gums), stop giving them MiraLAX and take them to the vet right away. If your cat has an underlying disease, such as kidney, heart, or endocrine disease, this will require extra monitoring when MiraLAX is given.

What to consider when giving your cat MiraLAX

Be aware of the following before and during MiraLAX use to keep your cat comfortable and safe.

1. Rule out an obstruction, which is an emergency. If there is any chance your cat has an intestinal blockage, you should never use MiraLAX. Warning signs include:

• No appetite

• Distended abdomen

• No bowel movement for 48-plus hours

• Frequent vomiting

• Straining without having a BM

2. Hydration is critical because MiraLAX works by drawing water into the colon.

• Feed wet food

• Provide fresh water at all times

• If your cat prefers running water, use a fountain

3. MiraLAX treats the symptom, not the cause. Constipation is a symptom, not a disease. There is always an underlying reason why your cat is suffering from constipation. Those reasons can include:

• Arthritis

• Neurologic dysfunction

• Hypothyroidism

• Dietary issues

• Kidney disease

• Pelvic narrowing

If your cat hasn’t been diagnosed with any of these conditions, but is having recurring constipation, it’s time for a veterinary exam.

4. Monitor stool quality. Every cat reacts differently to MiraLAX. Sometimes, after starting, your cat may develop diarrhea. That could mean you’re giving them too much and should decrease the dosage.

5. Avoid long-term use without guidance. Many cats use MiraLAX long-term with no problems, including those with megacolon, but they do need periodic monitoring to assess hydration and electrolyte status.

Alternatives to MiraLAX

If MiraLAX doesn’t solve your cat’s problem, there are other safe and effective options.

Lactulose

This is a stool softener in liquid form. Unfortunately, it’s very sweet and sticky, and cats often don’t like it. On the other hand, it can be very effective for chronic constipation.

Canned pumpkin

Pumpkin adds moisture and fiber. It’s very good for mild constipation, but it’s not strong enough for moderate or severe constipation. It is widely tolerated, natural, and gentle.

Fiber supplements (psyllium, Metamucil)

Fiber supplements are most useful for cats who need bulk in their stool. The advantage is that it can help regulate stool consistency. On the other hand, fiber can worsen constipation if the cat is not well-hydrated.

Prescription G.I. diets

Some diets are high in fiber or highly digestible and are available only by a vet’s prescription. They can be very good for long-term regulation. There is more than one brand, so you may have to try different ones to find the one which your cat will eat, and that helps them.

Motility medications (cisapride)

This can be helpful for motility disorders or megacolon. It works by increasing contractions. It is available by prescription only and through compounding pharmacies.

Hydration support

Subcutaneous fluids may be needed, especially if your cat has chronic kidney disease, although even just repeated constipation may necessitate it. 

Hydration alone can significantly improve bowel regularity. Adding water to wet food can help. Also, cats often will drink more if you use cat fountains instead of just bowls. 

Bottom line

MiraLAX can be very useful in managing constipation in cats and is safe and effective when given correctly. The usual dosage is one-eighth to one-fourth of a teaspoon once or twice daily, mixed into your cat’s canned food — and provided with plenty of water. You will usually see results in one to three days. Never use MiraLAX if you suspect an intestinal blockage. Also, recurrent constipation warrants a veterinary visit. If your cat has megacolon, MiraLAX can be beneficial, but your cat needs regular checkups with your vet.

Resources

• Benjamin, Sarah E, and Kenneth J Drobatz. “Retrospective Evaluation of Risk Factors and Treatment Outcome Predictors in Cats Presenting to the Emergency Room for Constipation.” Journal of Feline Medicine and Surgery, vol. 22, no. 2, 5 Mar. 2019, pp. 153–160. journals.sagepub.com/doi/10.1177/1098612X19832663.

• Tam, Fiona M, et al. “Safety and Palatability of Polyethylene Glycol 3350 as an Oral Laxative in Cats.” Journal of Feline Medicine and Surgery, vol. 13, no. 10, Oct. 2011, pp. 694–697. journals.sagepub.com/doi/10.1016/j.jfms.2011.05.017.

• Vca_corporate, ‌“Megacolon in Cats.” vcahospitals.com/know-your-pet/megacolon-in-cats.