My cat has diarrhoea: what now?

A healthy cat usually passes one or two firm, brown, well-formed stools a day. Diarrhoea (spelled diarrhea in American English) is softer, mushy or watery stool, sometimes passed more often or with straining.

It happens when stool moves through the gut too fast, so water, salts and nutrients are not absorbed. It is a sign of a digestive problem, not a disease on its own, and it can have many causes.

Diarrhoea is also a defence: the body tries to flush harmful germs or substances out of the gut. This is one reason anti-diarrhoea drugs are not helpful in every case and are not for owners to choose.

Vets call diarrhoea acute when it starts suddenly and lasts up to about three weeks, and chronic (long-lasting) when it lasts longer or keeps coming back. Sources differ a little on the cut-off, from two weeks to a month.

First check the cat. A bright cat that is eating, drinking and keeping food down and has had one or two loose stools is in a different place than a cat that is quiet, vomiting or has blood in the stool. The signs list on this page helps you decide.

Keep fresh water available all day, in more than one place and away from the food and the litter tray. Some cats drink more from a fountain or running tap. Mixing a little water into wet food also adds fluid.

Offer small, light, easily digested meals several times a day instead of large ones. Vets sometimes suggest a tinned food made for upset stomachs. Plain boiled chicken or white fish without skin, bone or seasoning is often mentioned as a short-term helper, but it is not a complete diet.

Do not starve the cat. A cat that does not eat is at risk of fatty liver disease, and the gut needs food to heal. If the cat refuses food, phone the vet. Some veterinary texts mention a short food pause of 12 to 48 hours; that is a vet's call for a particular cat and is not advised for kittens.

Do not give rich, fatty or salty food, table scraps, raw meat or milk. Many adult cats cannot digest the lactose in cow's milk, and milk is a common cause of diarrhoea. When the stool is firm again, bring the normal food back slowly over a few days, because a fast switch can start the diarrhoea again.

Food is the most common cause of a short episode: a sudden change of food (including from dry to wet or the other way round), new treats, overfeeding, or eating something unsuitable such as scraps, rubbish or plants. These episodes often settle within a few days. Milk or cream is also a known trigger, because many adult cats do not tolerate lactose.

Stress, such as a move, a new animal, a trip or a stay at the vet, speeds up digestion and can give a brief bout of loose stools. A stressed cat can also let an existing infection flare up. Food intolerance or food allergy causes long-lasting or recurring diarrhoea in some cats; estimates of how often food is behind chronic gut signs vary a lot between studies.

Parasites are a very common cause, above all in kittens and young cats: roundworms, hookworms, and single-celled parasites such as Giardia, coccidia, Cryptosporidium and Tritrichomonas. Infections can do it too: bacteria such as Salmonella and Campylobacter, and viruses such as feline panleukopenia (parvovirus), feline coronavirus, and FeLV or FIV. Several cats in one home getting ill together points to something infectious.

Medicines can cause diarrhoea. Antibiotics can upset the gut bacteria, and anti-inflammatory painkillers (NSAIDs) are a known cause. So can poisons, cleaning products and human medicines. A swallowed object such as string or thread can block the gut. If you suspect this, do not pull on the string and go to the vet.

Disease elsewhere in the body can show up as diarrhoea: pancreatitis, liver or kidney disease, diabetes, and an overactive thyroid (hyperthyroidism) in older cats. These cats usually have other signs too, such as weight loss with a big appetite, or drinking and weeing more. In middle-aged and older cats, long-lasting diarrhoea can come from inflammatory bowel disease (IBD) or from gut tumours such as lymphoma. These are diagnosed by the vet after other causes are ruled out.

A kitten can lose a lot of fluid in a very short time, dehydrates fast and can weaken quickly. Its gut is still adjusting to solid food, and its immune system is not fully developed. In kittens the usual causes are food or milk (formula made or dosed wrongly, cow's milk, overfeeding), worms and Giardia, other infections including panleukopenia, and stress after leaving the mother and moving home.

Older cats, sick cats, pregnant cats and cats with weak immunity are also more at risk of dehydration and of a hidden underlying disease.

Dehydration can lead to a salt imbalance and shock. Signs are dry or sticky gums, sunken eyes, loss of skin springiness, less energy, and not wanting to drink. Most diarrhoea in cats clears by itself, but severe or long diarrhoea left alone can lead to dehydration and serious illness.

The vet asks about the diet (including treats and supplements), how long it has lasted, how the stool looks (colour, amount, mucus, fresh blood), worming and vaccination history, other pets, and how the cat lives. Then the cat is examined for fever, dehydration, belly pain, weight and, in older cats, the thyroid in the neck.

Mild, sudden diarrhoea in an otherwise well cat is often treated without tests. Tests are kept for cats that relapse, are ill, or have long-lasting diarrhoea. A fresh stool sample is the first test. It looks for worms and Giardia, sometimes bacteria and viruses. Giardia cysts are shed on and off, so the vet may ask for samples over several days; a three-day pooled sample is one method.

A positive test does not always prove the cause. Many healthy cats carry Giardia and other organisms without being ill, so the vet looks at the whole picture.

For long-lasting or severe cases the vet may add blood and urine tests (including thyroid, and vitamin B12 and folate), tests for FeLV and FIV, an X-ray or an abdominal ultrasound, and sometimes a camera examination with a small tissue sample (biopsy). A kitten with diarrhoea and signs of illness is usually tested for panleukopenia (feline parvovirus).

The treatment follows the cause. Vets replace fluid and salts when a cat is dehydrated, by drip or injection under the skin, and may give anti-sickness medicine or pain relief.

A highly digestible, low-residue diet, or a veterinary intestinal diet, is the most usual first step. Added fibre helps some cats, above all with large-bowel diarrhoea. Vets sometimes advise a veterinary probiotic or a bowel-soothing product; the evidence for probiotics is mixed and the contents of products can differ from the label.

Antibiotics are rarely needed for diarrhoea in cats. They can upset the gut bacteria for a long time, so many vet guidelines keep them for cats with signs of blood poisoning or specific infections.

Worms and Giardia: the vet uses an anti-parasite medicine chosen for the cat, such as fenbendazole (a wormer) or sometimes metronidazole. The vet decides drug, dose and length. Treatment is usually combined with strict hygiene, and in a multi-cat home often all cats are treated together. A cat that tests positive for Giardia but is healthy usually needs no treatment. After treatment the vet may recheck the stool, because infection with Giardia can return and does not give lasting immunity.

Mild feline coronavirus diarrhoea needs only supportive care (fluids, a digestible diet). There is no specific antiviral. If the diarrhoea does not settle, the vet reconsiders the diagnosis and looks further, for example for other parasites, food intolerance, IBD, pancreas problems or thyroid disease.

Giardia is a tiny single-celled parasite of the small intestine. Cats catch it by swallowing cysts from the stool of other cats, contaminated water, food bowls, paws or fur. A few cysts are enough, and they can survive for weeks to months in damp surroundings.

Many cats with Giardia show nothing. When there are signs, they are usually soft, pale, smelly, sometimes slimy stool, with or without weight loss and a dull coat, mostly in kittens and young cats from groups such as shelters and catteries. Cat-to-person spread of Giardia is rare, but wash hands after handling faeces, and tell your doctor if you have similar symptoms, especially with weak immunity.

Diarrhoea can also follow worming for a short time. If it does not stop after treatment, the vet should check a stool sample. Keep to the worming plan the vet sets for the cat. If your kitten has diarrhoea, ask the vet whether the wormer should go on; see the worming page.

Diarrhoea that lasts about three weeks or longer, or keeps coming back, needs a step-by-step check by the vet rather than waiting it out. Common long-term causes are food intolerance, inflammatory bowel disease (IBD), chronic infections, an overactive thyroid, pancreas problems, and in older cats gut tumours. Signs can come and go, and diarrhoea may not be the first sign: vomiting, a smaller appetite or weight loss often come first.

A vet usually rules out other causes first, then tries a strict diet trial. Roughly half of the cats with IBD in one referral study improved on diet alone. The diet must be the only food, with no treats or flavoured medicine.

A definite diagnosis of IBD, or telling it from lymphoma, needs a gut biopsy under anaesthetic. Treatment is often long term and many cats do well for years, but flare-ups are common. IBD is more common in middle-aged and older cats. Siamese and some other Asian breeds are recognised as more prone, but any cat can be affected. Hyperthyroidism in older cats can cause diarrhoea (though vomiting and weight loss are more common). It is often reversible when the thyroid is treated.

Change food gradually over at least a week. With a kitten, mix the new food into the old step by step. Do not overfeed kittens; several small meals a day are gentler than one or two large ones.

Keep to the vet's worming and vaccination plan; vaccination protects against panleukopenia, an infection that causes severe diarrhoea.

Keep the litter tray and bowls clean, remove stool at least daily, and give each cat enough space. Where cats live together, hygiene limits the spread of Giardia and other intestinal infections. Keep poisons, cleaning products, string, plants and human medicines out of reach, and do not give human medicines or home remedies without asking the vet.