Vomiting and Diarrhoea in Cats: Causes and What Tests

Vomiting and diarrhoea are the most common gastrointestinal complaints in cats. Sometimes it is a one-off reaction (a hairball, a food change), and sometimes a sign of poisoning, infection or organ disease. In cats dehydration sets in fast, so it matters to tell the harmless from the dangerous in time. Let's break down the causes, what to do and what tests to run.

Common Causes of Vomiting and Diarrhoea in Cats

• Hairballs (trichobezoars) — a common cause of vomiting.
• Diet errors: a food change, overeating, intolerance.
• Parasites and infections (especially in kittens).
• Foreign body (thread, tinsel — dangerous!).
• Organ disease: GI tract, pancreas, liver, kidneys, hyperthyroidism.
• Toxins (many plants and human medicines are poisonous to cats).

When It Is Dangerous (Red Flags)

See a vet urgently if:

• vomiting with blood or repeated, diarrhoea with blood;
• the cat is lethargic, not drinking, hiding, with abdominal pain;
• it lasts more than a day or there is heavy dehydration (skin tents, dry gums);
• the cat is not eating alongside vomiting/diarrhoea — especially dangerous in cats (risk of hepatic lipidosis);
• a kitten or old cat — seek help sooner.

Vomiting White Foam, After Eating, Hairballs

White foam/bile on an empty stomach happens with an empty stomach; right after eating — overeating or gulping; periodic vomiting of a hairball is common, but if frequent or with diarrhoea, a work-up is needed. Any blood warrants a vet.

Cat Vomiting White Foam: When It Stops Being Harmless

White foam is not food but mucus and gastric juice, sometimes mixed with bile: the stomach is empty while its wall keeps working and getting irritated. Hence the three most common explanations. A long gap between meals — the classic morning vomiting in cats fed twice a day. A hairball the cat could not bring up whole, with foam arriving ahead of the hairball itself. Chronic gastritis, where an inflamed lining reacts to any emptiness in the stomach.

Such vomiting counts as harmless while it is a one-off, the cat is bright afterwards, eats and drinks as usual and holds its weight. It stops being harmless when episodes repeat for several days in a row or more than once a week; when the foam shows blood, brown coffee-ground specks or a lot of bile; when other changes join in — a lethargic cat that hides and refuses food; when diarrhoea runs alongside or, conversely, there is constipation in cats; when weight is lost.

What is examined is the cause, not the foam: a complete blood count and biochemistry with liver, kidneys and protein, thyroid hormones in cats over seven, a urinalysis, and an abdominal ultrasound if a foreign body or a thickened stomach wall is suspected. If fasting vomiting repeats and inflammation is confirmed, the ration is the next lever: the principles of gentle feeding are covered in gastritis and food allergy.

What to Do at Home (No Red Flags)

If the cat is active, the episode is a one-off, without blood: withhold food for a few hours, ensure water (dehydration is the main risk), then small portions of a bland diet. Do not give human medicines — many are toxic to cats. No improvement in a day or red flags appear — see a vet.

What Tests to Run

Baseline — a complete blood count and biochemistry (inflammation, liver, kidneys, dehydration) plus a stool test if needed; the blood breakdown is in cat blood test. If a foreign body is suspected — ultrasound for dogs and cats. If the cat refuses food — why a cat is not eating.

To understand your pet's tests in plain language, upload the form (PDF or photo) to the pet results interpretation service. This helps you understand the result but does not replace a vet.

If there are no tests yet and several behaviour changes have appeared at once, describe the whole picture on the cat symptoms page: the combination of signs shows what is worth running first.

This article is informational. Diagnosis and treatment of your pet are the job of a veterinarian.