Top 5 Prescription Diets for Cats with IBD Recommended by Veterinarians — Managing Chronic Vomiting and Diarrhea

DigestiveTop PicksMeongsiljang Veterinary Advisory Board

We compare five prescription diets for cats suffering from chronic vomiting and diarrhea due to inflammatory bowel disease (IBD). We cover the differences between hydrolyzed and novel protein diets, how to transition your cat to a new food, and important precautions—all in one place.

What Are Prescription Diets for Feline IBD?

Cat IBD prescription food served in a white bowl

Prescription diets for feline inflammatory bowel disease (IBD) are medically formulated foods precisely designed with specific protein structures, dietary fiber, and fat content to manage intestinal mucosal inflammation that causes chronic vomiting and diarrhea. The key feature is "avoidance of protein allergens." Unlike standard pet foods, these diets typically use hydrolyzed or novel protein sources to prevent the intestines from recognizing the protein as a threat. After a veterinary diagnosis, you must transition your cat to this single diet for at least 6 to 8 weeks to properly evaluate its effectiveness.

Why Are Prescription Diets Necessary?

Inflammatory Bowel Disease (IBD) is a condition characterized by the chronic infiltration of inflammatory cells, such as lymphocytes, plasma cells, and eosinophils, into the intestinal mucosa. Its causes are not singular; rather, it is understood to arise from complex interactions between the gut microbiota and the intestinal immune system. An abnormal immune response to dietary antigens (specific proteins) is also considered a significant contributing factor. Since standard commercial diets often contain common proteins like chicken, beef, or fish, the intestines of some cats with IBD may react hypersensitively to these ingredients. Prescription diets aim to calm this immune response by either breaking down these antigens into smaller components (hydrolysis) or substituting them with novel proteins that the cat has not previously consumed.

Comparison of the Top 5 Prescription Diets for Feline IBD

Item	Hill's z/d	Royal Canin Hypoallergenic HP	Purina HA	Royal Canin Selected Protein PR (Rabbit)	Hill's d/d Duck & Green Pea
Protein Type	Hydrolyzed chicken	Hydrolyzed soy protein	Hydrolyzed soy protein	Novel protein (rabbit)	Novel protein (duck)
Protein Content (Dry Matter)	Approx. 33%	Approx. 27%	Approx. 35%	Approx. 32%	Approx. 31%
Dietary Fiber	Moderate	Moderate	Low	Low	Moderate
Palatability	Moderate	Good	Moderate	Very good	Good
Price Range (2kg)	$50 to $60 range	$60 to $60 range	$60 range	$60 to $70 range	$60 to $60 range

Domestic average prices as of May 2026. Always purchase prescription diets after a veterinary diagnosis.

1st Place — Hill’s z/d (Hydrolyzed Chicken)

z/d is a hydrolyzed diet in which chicken protein is broken down into small peptide units that are difficult for the immune system to recognize as antigens. The key point is that the peptide size is smaller than the threshold required to trigger an immune response. It is one of the hydrolyzed prescription diets frequently chosen for elimination diet trials in cats with inflammatory bowel disease (IBD). Its advantage is that, as a single-protein-source diet, it ensures clear allergen avoidance. The drawback is that some cats may initially refuse to eat it due to the characteristic bitter taste of hydrolyzed proteins. Over the first two weeks, gradually transition by mixing the new food with the current diet in the following proportions: 25%, then 50%, then 75%, and finally 100% z/d.

A gray cat taking prescription medication

2nd Place — Royal Canin Hypoallergenic HP

This product is made from hydrolyzed soy protein and is suitable for cats with inflammatory bowel disease (IBD) who are suspected of having a chicken allergy. In a crossover blind study, 7 out of 10 IBD cats fed a hydrolyzed soy-based diet showed improvement, which was a better response compared to non-hydrolyzed prescription diets (3 out of 10 cats improved). The advantages are that it has relatively good palatability, so even picky eaters tend to enjoy it, and the small kibble size makes it easy to consume. The disadvantage is that it is ineffective for cats with an allergy to soy protein itself. Therefore, the typical approach is to start with z/d or PR (novel protein) diets for an elimination trial, and if the response is unclear, switch to HP.

3rd Place — Purina HA (Hydrolyzed)

Purina HA is also based on hydrolyzed soy protein. Weight loss is a common symptom of IBD, so it is important to provide a prescription diet that consistently supplies adequate nutrition. A low-fiber diet helps with stool management in cases of severe diarrhea by not increasing fecal bulk. However, since its distribution in Korea is limited to certain veterinary clinics, it may be difficult to obtain. If prescribed, please confirm the purchase location with your veterinarian in advance. Also, check whether vitamin B12 (cobalamin) supplementation is needed for long-term feeding—cats with IBD involving the ileum may develop cobalamin deficiency due to malabsorption.

Prescription diet food served in a stainless steel bowl

4th and 5th Place — Novel Protein Options

- 4th Place: Royal Canin Selected Protein PR (Rabbit): This novel ingredient diet uses rabbit protein as the sole protein source. It’s an excellent alternative for pets who struggle with hydrolyzed diets or refuse them. It also boasts exceptional palatability. - 5th Place: Hill's d/d Duck & Pea: This novel ingredient diet combines duck and pea proteins. It’s often recommended for pets with skin allergies accompanied by IBD. To maintain the effectiveness of a novel ingredient diet, it’s important to feed only that specific protein long-term, including treats and supplements.

Essential Precautions When Transitioning to a Prescription Diet

Prescription diets are harder to maintain than to start. During the 6- to 8-week food trial, you must strictly avoid giving any treats, milk, or human food in addition to the prescription diet. Even a single exposure to a different protein can trigger an immune response, forcing you to restart the six-week trial from the beginning. If symptoms do not improve on the prescription diet alone, it is likely that the issue is not a food-responsive intestinal disease. To rule out other conditions, such as lymphoma, an endoscopic biopsy may be necessary, so please consult your veterinarian about the next steps.

Feeding Tips to Maximize the Effectiveness of Prescription Diets

- Small, frequent meals: Instead of giving a large amount at once, divide the daily ration into four to five smaller meals. This reduces the burden on the stomach and decreases the frequency of vomiting. - Adequate hydration: Chronic diarrhea can easily lead to dehydration. Place multiple bowls of filtered water around the home or use an automatic water fountain to encourage drinking. - Monitor weight and stool: Weigh your pet weekly and take photos to record stool consistency (using a 1–7 scale). This allows for an objective assessment of how they are responding to the prescription diet. - Check Vitamin B12 levels: If there is no improvement after 6–8 weeks, have your pet’s blood cobalamin (Vitamin B12) levels tested. If a deficiency is found, injectable supplementation will be necessary.

A caregiver is feeding a small amount of prescription diet to a calico cat.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Will IBD be cured just by giving prescription food?

IBD is a condition where management, rather than a complete cure, is the primary goal. One study found that approximately 70% (7 out of 10) of cats with IBD showed symptom improvement when fed a hydrolyzed prescription diet, although some required additional treatment with immunosuppressants like prednisolone. If there is no improvement within 6 to 8 weeks on a prescription diet alone, further diagnostic evaluation is necessary.

Do I need to give this prescription medication for the rest of my pet’s life?

For dogs with confirmed food sensitivities, it’s safest to stick with the same protein source for life. Switching to a different protein increases the risk of symptoms returning. If you do need to change the protein source, always consult your veterinarian first.

My pet won’t take the prescribed medication. What should I do?

For the first two weeks, gradually transition by mixing the new food with the old in 25% increments. If your pet still refuses to eat it, try switching to a hydrolyzed or novel-protein diet. Never use human food or regular treats as rewards—this will invalidate the dietary trial.

Can I give my pet prescription medication and supplements together?

Vitamin B12 (cobalamin) can help correct deficiencies caused by malabsorption in cats with IBD that involves the small intestine. Probiotics may be considered as an addition to dietary and medical therapy, but their efficacy in feline IBD has not yet been established by research. Additionally, supplements containing protein, such as fish oil capsules with gelatin shells, can act as allergens, so please show the ingredient list to your veterinarian for verification.

What should I do on days when my pet is vomiting severely?

If your cat vomits three or more times within 12 hours, if you see blood or bile in the vomit, or if they refuse food and water for more than 24 hours, seek veterinary care immediately. Dehydration and electrolyte imbalances can quickly become dangerous for cats with inflammatory bowel disease (IBD).

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References

[1] Schaer M., Gaschen F., Clinical Medicine of the Dog and Cat, 4th Ed, Chapter on Chronic Enteropathies

[2] Ahn H. et al., Handbook of Veterinary Pharmacology, Section on Antiemetics and GI Drugs

[3] Jergens A.E., Feline idiopathic inflammatory bowel disease — what we know and what remains to be unraveled, Journal of Feline Medicine and Surgery, 2012