FrançaisCan cats drink milk?
It is better not to. Milk is not toxic, but veterinary sources do not recommend it as a treat, because it can upset a cat’s stomach [4] and many cats are lactose intolerant [3]. The ASPCA explains that pets do not have significant amounts of lactase, the enzyme that digests the sugar in milk, so milk and other dairy products can cause diarrhea or other digestive upset [2].
If your cat has lapped some milk, there is no emergency: watch the litter box over the next day or two. Kittens are a different case, covered below. Foods that are truly dangerous, such as onion, chocolate or lilies, are listed in toxic foods for dogs and cats.
Why many adult cats digest milk poorly
Lactose is the main sugar in milk. To be absorbed, it must first be split by lactase, an enzyme on the surface of the cells lining the small intestine [1]. Kittens have this enzyme to digest their mother’s milk. In cats, lactase activity declines after weaning, and they may become lactose intolerant; the Merck Veterinary Manual describes this relative lactase deficiency as the main inherited brush-border enzyme deficiency reported in cats [1].
Cats are carnivores and have less of these sugar-digesting enzymes than dogs. In one study, dogs had 3.1 times more lactase activity than cats in the first part of the small intestine and 1.6 times more in the middle part [5].
Intolerance is a matter of degree, not a rule for every cat. In a small study of 8 adult cats, a dry food containing 10% lactose did not change stool consistency [6]. Some cats tolerate a little dairy, others react to small amounts, and you cannot tell in advance. A gut that is already inflamed digests lactose even less well: damage to the intestinal lining can cause a secondary lactose intolerance, which is why dairy should be avoided in a cat with diarrhea [1].
Kittens: mother’s milk, milk replacer and cow’s milk
A kitten’s ideal food is its mother’s milk [8]. Weaning onto kitten food usually starts at around 3 to 4 weeks and is usually complete by around 8 weeks [12]. After that, kittens do not need milk.
For an orphan kitten, or when the mother is ill or does not have enough milk, a commercial kitten milk replacer is needed, and the ASPCA advises contacting your vet for the product and feeding plan [8]. Do not use cow’s milk: it can cause stomach upset and diarrhea in some kittens [8]. Cat milk is also very different from cow’s milk: one analysis measured about three times more fat in cat milk (110.8 mg/mL) than in cow’s milk (36.3 mg/mL) [9].
Commercial milk replacers are better than homemade versions, but none equals the mother’s milk [7]. Products also differ: in a 1993 study, kittens fed one commercial milk replacer of the time had diarrhea for most of the trial and developed lens opacities, linked to a low arginine level [10]. Overfeeding formula can itself cause diarrhea, often yellow and curdled [7]. Orphan kittens can deteriorate quickly and need close veterinary follow-up [11], so ask the vet before feeding and do not improvise a recipe.
What cats should drink: water first
Water is the drink cats need. Cats should have clean, fresh water at all times [3]. The Merck Veterinary Manual advises several water bowls, cleaned every day; wet food also helps, and a fountain may encourage some cats to drink [4]. Canned food contains at least 75% water, against 6 to 10% for dry food [3].
Other “milks” are not a better substitute. The ASPCA notes that the flesh and milk of fresh coconuts contain oils that may cause stomach upset, loose stools and diarrhea [2]. Raw milk and dairy of any kind should not be fed to cats [4]. Lactose-reduced products sold as “cat milk” exist; we found no veterinary study on them, so treat them as a treat, not as food or a replacement for water.
Any treat, milk-based or not, should stay small: the Merck Veterinary Manual sets treats at less than 10% of the daily calories [20]. And if your cat suddenly drinks and urinates a lot, talk to your vet: there might be a problem [4].
Intolerance or food allergy?
Lactose intolerance is not an allergy. It is a metabolic food reaction, not an immune one [13]. A true food allergy is an immune reaction to a protein in the food. In cats, the most common food allergens are beef, fish and chicken; dairy products are among the less common ones [13]. In a review of 78 cats with skin reactions to food, beef was involved in 18%, fish in 17%, chicken in 5%, and wheat, corn and dairy in 4% each [14].
Food can also cause chronic digestive signs. In a study of 55 cats with chronic digestive problems of unknown cause, 16 (29%) were food sensitive when tested with an elimination diet followed by a challenge [15]. A strict elimination diet followed by a rechallenge is the only reliable way to diagnose a food allergy [13]; blood tests do not replace it.
When diarrhea does not settle: what the vet checks
Most bouts of diarrhea in cats are short-lived, and a change of diet can cause a few days of loose stools [16]. Seek veterinary care as soon as possible if diarrhea lasts longer than a day or two and the cat also has a poor appetite, lethargy or vomiting, and do not give over-the-counter medicines, some of which are harmful to cats [16]. Diarrhea that goes on or keeps coming back can point to problems outside the gut, such as hyperthyroidism, kidney or liver disease, or lymphoma [16].
When digestive signs last 3 weeks or more, vets speak of a chronic enteropathy [17]. Laboratory tests are always needed to tell it apart from other diseases [18]:
| Test | What it looks for | Why it matters |
|---|---|---|
| Fecal analysis | Worms, Giardia and other parasites [17] | Parasites are ruled out first; Giardia can be missed because it is shed on and off [17] |
| Blood count, chemistry and urine | Signs of other diseases [18] | Part of the standard work-up; explained in cat blood work explained |
| Total T4 | Hyperthyroidism [18] | An overactive thyroid can cause diarrhea in older cats [16, 18] |
| Vitamin B12 (cobalamin) and folate | Poor absorption in the small intestine [17] | Low B12 is found in 18% to 80% of cats with chronic enteropathy [18]; in one study, 49 of 80 cats investigated for digestive problems had a low B12 [19]. A normal B12 does not rule out disease [18] |
| TLI | Exocrine pancreatic insufficiency [17] | The pancreas can be the cause, or a second problem [17] |
| Elimination diet trial | A food-responsive enteropathy [17] | A hydrolyzed or novel-protein diet fed exclusively for at least 2 weeks, with no treats of any kind [17] |
Weight loss is the most common sign of chronic gut disease in cats, and the absence of diarrhea does not rule out serious intestinal disease [18]. When tests and diet trials do not explain the signs, the vet may discuss imaging and biopsies, to separate inflammatory bowel disease from intestinal lymphoma; low B12 was particularly marked in cats with intestinal lymphoma [19].
Related articles
En français : lait et chat.
Questions to ask your veterinarian
- Could this diarrhea be due to dairy, or should we look for another cause?
- Which fecal tests do you recommend, and should we check for Giardia?
- Should we measure vitamin B12, folate and the thyroid hormone?
- Is an elimination diet trial worth doing, and for how long?
- For an orphan kitten: which milk replacer, and how should we check its weight?
Get your cat’s results explained.
AI DiagAnimals reads the blood count, chemistry, total T4, vitamin B12 and folate with your laboratory’s cat intervals, and prepares the questions for your vet. The service opens soon: leave your email to be told first.
Frequently asked questions
Is milk bad for cats?
It is not poisonous, but it is not recommended. Cats’ lactase activity falls after weaning and many adult cats become lactose intolerant [1, 3], so milk can cause diarrhea or digestive upset [2]. Some cats tolerate small amounts [6], but water is the better drink.
Can kittens drink cow’s milk?
No. Cow’s milk can cause stomach upset and diarrhea in some kittens [8]. Kittens need their mother’s milk or, if orphaned, a commercial kitten milk replacer chosen with the vet [7, 8].
What is the best liquid for cats to drink?
Fresh, clean water, available at all times [3]. Several bowls cleaned daily, wet food and a water fountain can help a cat drink more [4].
Can cats drink coconut milk?
It is not a good idea. The ASPCA notes that the flesh and milk of fresh coconuts contain oils that may cause stomach upset, loose stools and diarrhea [2].
Sources
- Collier A. Malabsorption Syndromes in Small Animals. Merck Veterinary Manual. merckvetmanual.com/digestive-system/diseases-of-the-small-intestine-in-small-animals/malabsorption-syndromes-in-small-animals
- ASPCA Animal Poison Control Center. People Foods to Avoid Feeding Your Pets. aspca.org/pet-care/aspca-poison-control/people-foods-avoid-feeding-your-pets
- Cornell Feline Health Center. Feeding Your Cat. vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/feeding-your-cat
- Roman N. Proper Nutrition for Cats. Merck Veterinary Manual, pet owner version. merckvetmanual.com/cat-owners/selecting-and-providing-a-home-for-a-cat/proper-nutrition-for-cats
- Batchelor DJ, Al-Rammahi M, Moran AW, et al. Sodium/glucose cotransporter-1, sweet receptor, and disaccharidase expression in the intestine of the domestic dog and cat. Am J Physiol Regul Integr Comp Physiol. 2011;300(1):R67-R75. doi.org/10.1152/ajpregu.00262.2010
- Beynen AC, Yu S. Magnesium balance in adult cats fed a dry food rich in lactose. J Anim Physiol Anim Nutr. 2003;87(7-8):245-250. doi.org/10.1046/j.1439-0396.2003.00397.x
- Davidson AP. Management of the Neonate in Dogs and Cats. Merck Veterinary Manual. merckvetmanual.com/management-and-nutrition/management-of-the-neonate/management-of-the-neonate-in-dogs-and-cats
- ASPCA. Cat Nutrition Tips. aspca.org/pet-care/cat-care/cat-nutrition-tips
- Chen Y, Yang J, Wang C, et al. Comparative Analysis of Signature Lipid Structures in Canine and Feline Milk Compared with Bovine and Caprine Milk. Animals (Basel). 2026;16(5):710. doi.org/10.3390/ani16050710
- Remillard RL, Pickett JP, Thatcher CD, Davenport DJ. Comparison of kittens fed queen’s milk with those fed milk replacers. Am J Vet Res. 1993;54(6):901-907. pubmed.ncbi.nlm.nih.gov/8323060
- Little S. Playing mum: successful management of orphaned kittens. J Feline Med Surg. 2013;15(3):201-210. doi.org/10.1177/1098612X13477542
- International Cat Care. Feeding your cat or kitten. icatcare.org/advice/feeding-your-cat-or-kitten
- Pucheu-Haston CM. Cutaneous Food Allergy in Animals. Merck Veterinary Manual. merckvetmanual.com/integumentary-system/food-allergy/cutaneous-food-allergy-in-animals
- Mueller RS, Olivry T, Prélaud P. Critically appraised topic on adverse food reactions of companion animals (2): common food allergen sources in dogs and cats. BMC Vet Res. 2016;12:9. doi.org/10.1186/s12917-016-0633-8
- Guilford WG, Jones BR, Markwell PJ, et al. Food sensitivity in cats with chronic idiopathic gastrointestinal problems. J Vet Intern Med. 2001;15(1):7-13. pubmed.ncbi.nlm.nih.gov/11215916
- Cornell Feline Health Center. Diarrhea. vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/diarrhea
- Collier A. Chronic Enteropathies in Small Animals. Merck Veterinary Manual. merckvetmanual.com/digestive-system/diseases-of-the-small-intestine-in-small-animals/chronic-enteropathies-in-small-animals
- Marsilio S, Freiche V, Johnson E, et al. ACVIM consensus statement guidelines on diagnosing and distinguishing low-grade neoplastic from inflammatory lymphocytic chronic enteropathies in cats. J Vet Intern Med. 2023;37(3):794-816. doi.org/10.1111/jvim.16690
- Simpson KW, Fyfe J, Cornetta A, et al. Subnormal concentrations of serum cobalamin (vitamin B12) in cats with gastrointestinal disease. J Vet Intern Med. 2001;15(1):26-32. pubmed.ncbi.nlm.nih.gov/11215907
- Sanderson SL. Feeding Practices in Small Animals. Merck Veterinary Manual. merckvetmanual.com/management-and-nutrition/nutrition-small-animals/feeding-practices-in-small-animals
Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.