Long-Term Diarrhea in Cats: Causes and Next Steps
By Dr. Zubair Khalid, DVM, MS, PhD ·
Long term diarrhea in cats means loose stool that keeps coming back for weeks or months, and it is a medical problem, not a sensitive stomach. Common causes include intestinal parasites, inflammatory bowel disease, food allergy, lymphoma, and thyroid disease. This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- Diarrhea lasting more than 3 to 4 weeks needs a veterinary workup, not just a diet change at home.
- The first steps are usually a fecal test, blood work, and a diet trial.
- Parasites such as Tritrichomonas foetus and Giardia are common and treatable causes of chronic large bowel diarrhea [1][2].
- Diet is a core part of treatment, not an add-on, and many cats improve on a prescription or hydrolyzed diet [3][4].
- Some cats need medication, and the choice depends on the exact cause found during testing.
What Long Term Diarrhea in Cats Actually Means
Chronic diarrhea is a common clinical sign in cats, and it can come from many different underlying conditions [3]. Vets divide it into two types based on where the problem sits: small bowel diarrhea and large bowel diarrhea [3]. The large intestine absorbs water and salts, stores stool, and supports healthy gut bacteria, so when it is damaged by illness or parasites, diarrhea is often the result [5].
The two types look different at home. Small bowel diarrhea tends to produce large volumes of stool, often with weight loss. Large bowel diarrhea tends to produce small, frequent stools, sometimes with mucus or fresh blood, and the cat may strain. Knowing which pattern your cat has helps your vet narrow the list of causes.
Chronic colitis, which is inflammation of the colon, is one form of this problem. Cats with chronic colitis tend to be middle-aged and are often purebred [5]. In most cases the cause is unknown, though bacterial, parasitic, traumatic, kidney-related, and allergic causes are suspected [5].
Signs Owners Notice
The obvious sign is loose stool that does not fully resolve. Beyond that, watch for:
- Stool frequency and urgency, especially small amounts many times a day
- Mucus or bright red blood on the stool
- Straining in the litter box, which owners sometimes mistake for constipation
- Weight loss, even if your cat still eats well
- Dull coat, low energy, or hiding more than usual
- Vomiting, which can happen alongside the diarrhea
- Accidents outside the litter box
If your cat has diarrhea after eating a specific meal, that timing can be a clue. Our guide to cat diarrhea after eating covers that pattern in more detail.
Causes and Risk Factors
Parasites
Tritrichomonas foetus is a protozoan parasite that causes large bowel disease in cats worldwide [1]. In one study of 1,606 feline stool samples, T. foetus DNA was found in 10.6% of cats with diarrhea reported within the last 6 months, and the highest rate (14.9%) was in cats younger than one year [1]. This parasite should be part of the testing plan for any cat with large bowel diarrhea [1]. Giardia is another common finding, detected in 8.4% of samples in a large chronic diarrhea study [2].
Inflammatory Bowel Disease and Chronic Enteropathy
Chronic enteropathy is the broad term for long-term gut inflammation. The immune system in the colon may be reacting too strongly to dietary or bacterial factors, and genetics or past infections may play a role [5]. This is one of the most common reasons a cat has soft stool for months.
Food Allergy and Food-Responsive Disease
Some cats improve when the protein source in their diet changes. A diet trial is both a treatment and a diagnostic tool, and your vet may use specific foods to help identify the cause [5].
Lymphoma and Other Cancers
Gastrointestinal lymphoma is a serious cause of chronic diarrhea and weight loss in older cats. Feline gastrointestinal eosinophilic sclerosing fibroplasia is a less common inflammatory condition that can form masses in the gut and, rarely, spread to the liver and lymph nodes [6]. It can be mistaken for a tumor, so biopsy is often needed to tell them apart [6].
Thyroid Disease
Hyperthyroidism speeds up the digestive tract and can cause chronic diarrhea, weight loss despite a good appetite, and vomiting. It is diagnosed with a simple blood test.
Other Causes
Large intestinal disease in cats can also come from infectious agents, inflammatory disease, tumors, blood vessel problems, and motility disorders [7]. Feline coronavirus was found in 65.1% of cats with chronic diarrhea in one large study, often alongside other pathogens, though its exact role in causing the diarrhea is still debated [2].
| Cause | Typical Clues | Main Test |
|---|---|---|
| Parasites (T. foetus, Giardia) | Large bowel diarrhea, young cat, mucus | Fecal PCR or special fecal testing [1][2] |
| IBD or chronic enteropathy | Months of soft stool, weight loss, middle-aged cat | Blood work, ultrasound, biopsy [5] |
| Food allergy | Itching, vomiting, stable weight | Diet trial [5] |
| Lymphoma | Older cat, weight loss, thickened gut on ultrasound | Biopsy [6] |
| Hyperthyroidism | Ravenous appetite, weight loss, fast heart rate | Thyroid blood test |
How It Is Diagnosed
Your vet starts with detailed questions about your cat's history and a full physical examination [5]. Bring notes on stool frequency, appearance, diet changes, and any medications.
Expect some or all of these tests:
- Fecal testing, including PCR panels for parasites such as T. foetus and Giardia [1][2]
- Blood work and a urine sample to check organ function and thyroid level [5]
- Abdominal x-rays or ultrasound to look at the intestines and other organs [5]
- Diet trials with specific foods, which can both diagnose and treat some causes [5]
- Endoscopy or biopsies when the cause is still unclear [5]
Colonoscopy with mucosal biopsy is used when other tests do not give an answer [7]. A biopsy is the only way to confirm lymphoma or eosinophilic sclerosing fibroplasia, since these conditions can look like tumors on imaging [6].
Treatment Options
Treatment is aimed at the underlying cause, supported by diet changes and supportive care [7].
Diet
Nutritional management is essential for long-term control of chronic diarrhea [3]. Options include hydrolyzed diets, limited ingredient diets, and high-protein, low-carbohydrate therapeutic diets. In one reported case, a cat with chronic nonresponsive enteropathy and diabetes improved after being switched to a high-protein, low-carbohydrate commercial veterinary therapeutic diet with mixed protein sources, and insulin was discontinued at discharge after 6 days in the hospital [4]. Soft stools can still take months to fully normalize even when the cat is improving [4]. Psyllium husk was later added in that case to improve stool quality [4].
Medication
- Antiparasitic drugs when a parasite is found. In one report, two cats with T. foetus were treated with tinidazole at 30 mg/kg [8]. Never use this number on your own cat. Your veterinarian calculates the dose from your pet's weight and health.
- Corticosteroids or other immune-suppressing drugs for inflammatory disease [6]
- Antibiotics for specific bacterial infections
- Thyroid medication for hyperthyroidism
- Chemotherapy for lymphoma
Supportive Care
Cobalamin (vitamin B12) injections are often used when the gut is not absorbing nutrients well [4]. Your vet may also recommend probiotics, fiber supplements, or fluids depending on your cat's condition.
If your cat's diarrhea started after a new prescription, read our article on cat diarrhea after starting a new medication.
Recovery, Outlook, and Long-Term Management
The outlook depends on the cause, how severe it is, and how quickly treatment starts [7]. Parasite infections often clear with the right drug. Food-responsive disease can go into remission with diet alone. IBD usually needs ongoing management with diet, medication, or both. Lymphoma has a more guarded outlook and needs cancer treatment.
Plan for a long haul. Soft stools may persist for several months even after treatment begins, with gradual improvement over time [4]. Keep a simple log of stool quality, appetite, weight, and any vomiting. Bring it to every recheck. Weigh your cat at home if you can, since weight loss is one of the most useful signals that treatment is or is not working.
If your cat swings between diarrhea and hard stool, see cat constipation after diarrhea for what that pattern can mean.
Prevention
You cannot prevent every cause, but you can lower the odds:
- Keep your cat indoors to reduce exposure to parasites and infectious disease
- Use veterinarian-recommended parasite prevention year-round
- Introduce new foods slowly and one change at a time
- Keep up with routine wellness visits, especially as your cat ages
- Treat intestinal infections promptly so chronic inflammation does not set in
- Manage diagnosed conditions such as hyperthyroidism consistently
Limitations and When to Contact a Veterinarian
No article can replace an exam, and every cat with long term diarrhea needs a veterinarian to sort out the cause.
Contact your vet the same day if your cat:
- Has blood in the stool or black, tarry stool
- Is vomiting repeatedly or cannot keep water down
- Seems painful when you touch the belly
- Has a sudden drop in appetite or stops eating
Go to an emergency clinic now if your cat:
- Is weak, wobbly, or collapsing
- Has pale gums or a fast, weak pulse
- Is straining to defecate with nothing coming out and seems blocked
- Has a swollen, hard abdomen
Schedule a routine visit soon if the diarrhea has lasted more than 3 to 4 weeks, if your cat is losing weight, or if home diet changes have not helped.
Frequently Asked Questions
Can chronic diarrhea in cats go away on its own?
Sometimes mild cases from a short-term upset resolve without treatment, but diarrhea lasting months rarely clears on its own. Long-term diarrhea usually points to an ongoing cause such as parasites, inflammation, or cancer that needs diagnosis and treatment [3][7]. Waiting too long can let weight loss and nutrient deficiencies get worse.
Is long term diarrhea in cats always a sign of cancer?
No, cancer is only one of many possible causes. Parasites, food reactions, inflammatory bowel disease, and thyroid disease are all common and treatable [5][3]. Your vet uses testing to tell these apart, and a biopsy is usually needed before lymphoma can be confirmed [6].
What should I feed a cat with chronic diarrhea?
Your veterinarian should choose the diet, because the right food depends on the cause. Options include hydrolyzed diets, limited ingredient diets, and high-protein, low-carbohydrate therapeutic diets [3][4]. A diet trial is also a diagnostic tool, so it needs to be done carefully with no extra treats or table food [5].
Do I need to bring a stool sample to the appointment?
Yes, a fresh stool sample is very helpful. Fecal testing is a core part of the workup, and some parasites such as T. foetus require specific tests like PCR to be found [7][1]. Collect a sample within a few hours of the visit and keep it in a clean container.
How long does treatment take before I see improvement?
Some cats improve within days, while others take weeks to months. In one reported case, clinical signs improved gradually over 5 days, but soft stools persisted for several months before normalizing [4]. Your vet will set recheck intervals based on your cat's specific diagnosis and response.
Related Articles
- Cat Diarrhea After Eating: Causes and When to Act
- Cat Diarrhea: Causes, Home Care, and When to Worry
- Cat Constipation After Diarrhea: Causes and Relief
- What to Do If Your Cat Has Diarrhea After Starting a New Medication
- Kitten Diarrhea: Causes, Safe Home Care, and Emergency Signs
- Cat Diarrhea with Worms: Causes and Treatment Options
- Chronic Diarrhea in Cats With No Other Symptoms
- Why Does My Cat Keep Getting Diarrhea? Causes and Next Steps
- Uncontrollable Diarrhea in Cats: Causes and What to Do
- Intestinal Parasites in Dogs and Cats: Identification, Symptoms, and Treatment Options
References
- Prevalence of Tritrichomonas foetus Among Cats in Poland Between 2020 and 2024. Pathogens (Basel, Switzerland), 2025.
- Feline Coronavirus Prevalence in 493 Cats With Chronic Diarrhea. Journal of veterinary internal medicine, 2025.
- Feline chronic diarrhea: causes and nutritional management. Veterinary and animal science, 2026.
- Nutritional management of feline chronic enteropathy with evolving dietary response and long-term stabilization. The Canadian veterinary journal = La revue veterinaire canadienne, 2026.
- Disorders of the Stomach and Intestines in Cats - Cat Owners. Merck Veterinary Manual.
- A case of feline gastrointestinal eosinophilic sclerosing fibroplasia extending to the liver and jejunal lymph nodes. The Canadian veterinary journal = La revue veterinaire canadienne, 2025.
- Large-Intestinal Disorders in Dogs and Cats: Diagnosis, Management, and Clinical Outcomes. The Veterinary clinics of North America. Small animal practice, 2026.
- First report of Tritrichomonas foetus in cats from Northeastern Brazil. Veterinary research communications, 2025.