# Miralax for Cats Dosage : A Safe Guide Constipation in cats is common, and many owners ask about using Miralax (polyethylene glycol 3350) at home. There is no single safe over-the-counter dose you can look up and give on your own. The right amount depends on your cat's weight, hydration, and overall health, and a veterinarian should set it. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Miralax is polyethylene glycol 3350 (PEG 3350), an osmotic laxative that pulls water into the colon to soften stool [1]. - There is no published per-pound dose chart for cats that you can safely apply at home. Effective doses vary widely between individual cats, so dosing must be individualized [1]. - A veterinarian calculates the dose from your cat's weight and health status, then adjusts it based on stool consistency. - Always mix the powder into wet food or a small amount of water. Never give it dry, and never give it as a bolus syringe of powder. - Call your veterinarian or a poison control hotline right away if your cat gets too much, stops eating, vomits, or seems weak. ## What Miralax Is and What Veterinarians Use It For Miralax is the brand name for polyethylene glycol 3350, often shortened to PEG 3350. It is a white powder that dissolves in liquid. In cats, veterinarians use it most often for recurrent constipation that has not responded to diet changes alone [1]. Constipation in cats can range from occasional hard stools to severe fecal impaction, where stool cannot pass at all. A related product, polyethylene glycol-electrolyte solution (PEG-ES, sold as GoLYTELY), is used in more serious cases. One report described a cat with severe fecal impaction after surgery that did not respond to common medical management. PEG-ES given through an esophageal feeding tube resolved the impaction quickly, and the same approach later managed the cat's chronic constipation long term [2]. That case involved a veterinary procedure, not home treatment. It shows that polyethylene glycol products have a real place in feline medicine, but the choice of product, route, and dose belongs to a veterinarian. Diet also matters. A six-month controlled trial found that a gastrointestinal diet containing 6% psyllium was effective for managing chronic constipation in cats [3]. For many cats, fiber and water intake do more long-term good than any laxative. ## How Miralax Works PEG 3350 is an osmotic laxative. It stays largely in the gut and holds water in the stool, which softens the stool and makes it easier to pass [1]. Because it works by water movement, hydration matters. A cat who is dehydrated or not drinking well has less water available for the medicine to pull into the colon. This is also why giving too much is not harmless. A large dose can draw too much fluid and electrolyte into the gut. In a study of normal cats given PEG 3350 for four weeks, all cats achieved soft stools, and mild hyperkalemia (slightly high potassium) was seen without clinical signs. The cause of that potassium change is unknown [1]. ## Miralax for Cats Dosage Per Pound: What Owners Need to Know ### Who decides the dose Your veterinarian decides the dose. There is no standard miralax for cats dosage per pound that applies to every cat. In the four-week safety study, effective doses varied widely among the cats, and the authors concluded that individualized dosing is important [1]. That finding is the main reason you should not copy a number from a forum or a random chart. When your vet sets a dose, they consider your cat's weight, body condition, hydration, kidney function, current medications, and how severe the constipation is. They may start low and increase slowly. They may also ask you to track stool consistency at home so the dose can be fine-tuned. ### How it is given Mix the measured powder into a small amount of wet food, or dissolve it in a little water and mix that into food. Offer it in a meal your cat will finish so you know the full dose was eaten. If your cat eats only part of the food, do not guess and add more. Call your vet for guidance. Never blow powder into your cat's mouth or syringe a dry paste. Powder can be inhaled, and aspiration of polyethylene glycol-electrolyte solution into the lungs caused chemical pneumonitis and lung injury in one cat, requiring 10 days in intensive care [4]. That report involved a liquid electrolyte solution, but the lesson applies to anything you put near a cat's airway. Keep all of it in food or water, never near the nose or throat. ### Missed dose If you miss a dose, give the next dose at the normal time. Do not double up. Doubling can cause diarrhea, dehydration, and electrolyte problems. If you are unsure how to handle a missed dose, call your veterinary clinic. They handle this question every day. ### Other medicines your vet may mention Constipation is sometimes linked to other conditions, and your cat may be on more than one medicine. If your cat takes ursodiol for liver or gallbladder support, that dose is also calculated by weight and health status, and it is not something to adjust on your own. The same principle applies to any drug: the veterinarian sets the number. If your cat needs an antibiotic or an appetite stimulant, weight-based dosing guides exist for those too, such as this [amoxicillin dose guide for dogs and cats](/knowledge/veterinary-medicine/calculators-clinical-tools/amoxicillin-dog-cat-dose-broad-spectrum-antibiotic-weight-based-guide) and this [mirtazapine appetite stimulant guide](/knowledge/veterinary-medicine/calculators-clinical-tools/mirtazapine-appetite-stimulant-dose-for-cats-and-dogs-guide). Never swap doses between medicines. ## Side Effects to Watch For | Side effect | How common or serious | What to do | |---|---|---| | Soft stools or mild diarrhea | Expected when the dose is working, common | Keep feeding, note the stool, and tell your vet at the next check-in | | Mild high potassium without symptoms | Seen in a four-week study of normal cats, cause unknown [1] | Report it if your vet runs bloodwork, no home action needed | | Vomiting, poor appetite, lethargy | Not expected, potentially serious | Stop the medicine and call your vet the same day | | Weakness, wobbling, seizures, collapse | Rare but serious, seen with severe electrolyte and kidney problems after a large PEG 3350 exposure [5] | This is an emergency, go to a veterinary hospital now | | Coughing, trouble breathing after any oral liquid | Rare but serious, aspiration can cause lung injury [4] | Emergency care now | A note on the serious end of that table. In one report, a cat accidentally received 6 g/kg of PEG 3350 intravenously, which is a route never used for this medicine at home. The cat developed severe hypernatremia (a sodium level of 203 mmol/L), diffuse brain dysfunction, red blood cell destruction, and moderate kidney injury. Supportive care corrected the problems, and the cat recovered fully by one month after discharge [5]. That was an intravenous accident, not an oral overdose, but it shows how much harm a large polyethylene glycol exposure can do. ## Who Should Not Take It and Drug Interactions Miralax is not right for every cat. Your veterinarian may avoid it or use it only with close monitoring if your cat: - Is dehydrated or has been vomiting - Has kidney disease or a history of electrolyte problems - Has a suspected or confirmed bowel obstruction - Has megacolon that is not being managed by a vet - Is a kitten or is very underweight Tell your vet about every medicine and supplement your cat takes, including other laxatives, stool softeners, and prescription diets. Using two laxatives at once can cause severe diarrhea and dehydration. Do not add fiber, psyllium, or a new diet on your own while your cat is on Miralax unless your vet approves it. A psyllium-enriched diet helped cats with chronic constipation in a controlled trial [3], but diet changes and laxatives need to be coordinated. If your cat takes any medication for behavior, allergies, or appetite, mention it. Even common drugs like diphenhydramine have their own weight-based rules, as covered in this [Benadryl dosage and safety guide for cats](/knowledge/veterinary-medicine/pet-medication-guide/cat-benadryl-dosage-safety). Supplements count too, including melatonin, which is covered in this [guide to melatonin safety and dosing for cats](/knowledge/veterinary-medicine/vet-visit-decisions/can-i-give-my-cat-melatonin). ## Overdose and When to Call for Help If your cat ate more Miralax than intended, call your veterinarian or a pet poison control hotline right away. Do not wait for symptoms. Early signs of a large exposure can include vomiting, diarrhea, weakness, and wobbling. Severe cases can involve brain signs and kidney injury, as seen after a massive PEG 3350 exposure in one cat [5]. Have this information ready: your cat's weight, the product name, the amount given, and the time it was given. Keep the container so you can read the label. If your cat is having a seizure, cannot stand, is breathing hard, or is unresponsive, go to an emergency hospital now. Do not try to make your cat vomit at home. ## Limitations and When to Contact a Veterinarian This article cannot tell you the right dose for your cat. Every cat needs an individual plan made by a veterinarian who knows the cat's history and can examine it. Call your veterinarian the same day if your cat: - Has not had a bowel movement in 48 hours or is straining with nothing coming out - Vomits, refuses food, or seems painful in the belly - Has diarrhea that lasts more than a day on the medicine - Seems weak, wobbly, or unusually quiet Go to an emergency clinic now if your cat: - Is crying out or pacing in pain - Has a hard, bloated belly - Is breathing fast or open-mouthed - Collapses, seizures, or cannot be woken Schedule a routine visit if the constipation keeps coming back, if you are constantly adjusting the dose, or if your cat is losing weight. Recurrent constipation often points to an underlying problem that needs testing. Unexplained weight loss in cats is a reason to book an exam, and this [weight loss guide for cats](/knowledge/veterinary-medicine/nutrition/weight-loss-for-cats) explains what your vet will look at. ## Frequently Asked Questions ### Can I give my cat Miralax without seeing a vet? No, you should not start it on your own. Miralax is generally well tolerated in healthy cats when dosed correctly [1], but the correct amount varies from cat to cat and depends on hydration, kidney function, and other medicines. A short exam and a stool history let your vet choose a safe starting point. ### How long does it take for Miralax to work in a cat? Softening usually shows up within a day or two of starting the right dose. If your cat has not passed stool within about 48 hours, or is straining and uncomfortable, call your vet instead of adding more medicine. ### Can I mix Miralax with dry food? Wet food or a little water is the better choice. Dry food may not hold the powder evenly, so your cat could get a full dose in one bite and none in another. Mix it into a small portion your cat will finish. ### Is Miralax the same as the bowel prep my vet uses? No. Miralax is plain polyethylene glycol 3350. Bowel prep products are polyethylene glycol-electrolyte solutions, which contain added salts and are used under veterinary supervision for impaction and chronic constipation [2]. They are not interchangeable at home. ### What if my cat has kidney disease? Tell your vet before giving any laxative. Osmotic laxatives shift water and electrolytes, and cats with kidney disease are more prone to dehydration and electrolyte imbalance. Your vet may choose a different plan or monitor bloodwork closely. ### Can Miralax cause high potassium in cats? A mild rise in potassium without symptoms was seen in normal cats given PEG 3350 for four weeks, and the cause is unknown [1]. It was not linked to any illness in that study, but it is one more reason your vet may want bloodwork during long-term use. ## Related Articles - [Amoxicillin Dog Cat Dose: Broad-Spectrum Antibiotic Weight-Based Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/amoxicillin-dog-cat-dose-broad-spectrum-antibiotic-weight-based-guide) - [Can You Give Your Cat Benadryl? Dosage and Safety Guide](/knowledge/veterinary-medicine/pet-medication-guide/cat-benadryl-dosage-safety) - [Mirtazapine Appetite Stimulant: Dose for Cats and Dogs Guide](/knowledge/veterinary-medicine/calculators-clinical-tools/mirtazapine-appetite-stimulant-dose-for-cats-and-dogs-guide) - [Can I Give My Cat Melatonin? Safety, Dosage, and When to Avoid It](/knowledge/veterinary-medicine/vet-visit-decisions/can-i-give-my-cat-melatonin) - [Weight Loss For Cats](/knowledge/veterinary-medicine/nutrition/weight-loss-for-cats) - [Methimazole Cat Dose: Feline Hyperthyroidism Dose and Monitoring](/knowledge/veterinary-medicine/calculators-clinical-tools/methimazole-cat-dose-feline-hyperthyroidism-dose-and-monitoring) - [Miralax for Cats Side Effects: Risks and Warning Signs](/knowledge/veterinary-medicine/pet-medication-guide/miralax-for-cats-side-effects) - [Miralax for Dogs: Dosage](/knowledge/veterinary-medicine/pet-medication-guide/miralax-for-dogs-dosage-chart) - [Pepto Bismol for Cats Dosage: Is It Safe ?](/knowledge/veterinary-medicine/pet-medication-guide/pepto-bismol-for-cats-dosage) ## References 1. [Safety and palatability of polyethylene glycol 3350 as an oral laxative in cats](https://pubmed.ncbi.nlm.nih.gov/21820925/). Journal of feline medicine and surgery, 2011. 2. [Use of polyethylene glycolelectrolyte solution (GoLYTELY) for management of acute fecal impaction and chronic constipation in a cat](https://pubmed.ncbi.nlm.nih.gov/41716503/). The Canadian veterinary journal = La revue veterinaire canadienne, 2026. 3. [A psyllium-supplemented gastrointestinal diet is effective for the management of chronic constipation in cats: a 6-month controlled clinical trial](https://pubmed.ncbi.nlm.nih.gov/41631677/). Journal of feline medicine and surgery, 2026. 4. [Chemical pneumonitis secondary to accidental pulmonary polyethylene glycol-electrolyte solution infusion in a cat](https://pubmed.ncbi.nlm.nih.gov/38696695/). Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001), 2024. 5. [Severe hypernatremia and transient azotemia in a cat following inadvertent intravenous administration of a commercial polyethylene glycol solution](https://pubmed.ncbi.nlm.nih.gov/31471940/). Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001), 2019. ## Further Reading - [American Veterinary Medical Association: First Aid Tips for Pet Owners](https://www.avma.org/resources-tools/pet-owners/emergencycare/first-aid-tips-pet-owners) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information)