Why Do Cats Eat Grass?

Feral tabby cat eating grass
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From laxative effects to dietary needs, the theories behind why cats eat grass are as varied as they are uncertain. However, recent research may point to a more practical and instinctual reason for this behavior: cats eat grass because non-digestible plants purge their systems of parasitic worms. Of course, most contemporary house cats are not worm-infested, but this penchant for grass-eating goes back to their not so distant past as wild animals, when they consumed almost entirely raw meat.

Do All Cats Eat Grass?

Not all cats eat grass, but it is a pretty common behaviorIn a survey of 1,021 cat owners who observed their cat's behavior for at least three hours per day, 71% saw their cat eat grass at least six times.

Until the 21st century, the prevailing explanation for plant-eating has been that because cats cannot digest grass, they eat it when they are feeling ill and want to induce vomiting. Another popular theory argues that cats eat grass to supply fiber or because they're feeling anxious. While researchers are not always entirely certain why cats eat grass, recent data on both cats and dogs points away from grass-eating as a way to induce vomiting — with more than 90% of cat owners reporting that their pet does not appear ill before eating plants. If a plant is both nontoxic and not treated with pesticides, it's generally safe for cats to consume in moderation.

Eating Grass Is an Instinctual Behavior

Cats seem to have an innate predisposition toward regular plant eating, supported by numerous reports of wild carnivores eating plants, as shown mostly by the non-digestible grass and other plant parts found in their feces. Studies on primates reveal that non-digestible plants purge the intestinal system of helminthic (worm) parasites. According to researchers at the School of Veterinary Medicine at UC Davis, "Virtually all wild carnivores carry an intestinal parasite load, and regular, instinctive plant eating would have an adaptive role in maintaining a tolerable intestinal parasite load, whether or not the animal senses the parasites."

The researcher's findings indicating that 91% of cats do not appear ill before vomiting reinforce the theory that grass-eating is instinctual and helps cats purge harmful parasites, but doesn't happen because cats intentionally want to throw up. Nonetheless, 27% of cat owners surveyed reported their cat frequently vomiting after eating plants, with the percentage increasing as cats age.

Grass as a Laxative or Dietary Aid

Veterinarians have long wondered if cats eat grass as the result of a dietary deficiency — because of the vitamins and minerals present in different plants. Some have also theorized that grass could function as a sort of laxative, helping hairballs make their way through the digestive tract. Because research indicates that animals do not appear visibly ill before consuming grass, it's likely that grass-eating for these reasons would be another instinctual activity that dates back to their time in the wild, when cats consumed animals whole.

Eating grass
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More research needs to be done, but one study showed that consumption of prey in its entirety may provide components that aid in digestion and gastrointestinal health for felines, and are not present in commercially-prepared foods. Could grass eating be an effort on the part of cats to replace this missing dietary component?

It Relieves Stress and Anxiety

Any changes in a cat's behavior could mean that it is experiencing stress and anxiety, including excessive meowing, restlessness, irritability, scratching, and/or urination. Chewing can also be a reaction to stress in cats, and occasionally that could manifest in eating grass. While not necessarily a sign of illness, if your cat does not typically eat grass and then starts, a trip to the vet could be in order.

Is Eating Grass Bad for Cats? Risks

Eating grass in moderation is normal for the majority of cats and dogs, and is generally not associated with illness or an unhealthy gastrointestinal tract. Most risks come from potentially toxic plants as well as yards and gardens that have been treated with pesticides and herbicides.


Always check the American Society for the Prevention of Cruelty to Animals' (ASPCA) list of poisonous plants to find out if a plant is safe for your pet before bringing the plant into your pet's environment.

One option for cats who love to eat grass is to purchase catnip or wheat grass seeds that grow easily from a window indoors. Keep in mind that, when consumed in moderation, these plants won't harm your pet, but they still won't be able to digest them and could throw up. Some cats may also have an allergic reaction to grass, particularly if it gets stuck in their sinus cavity. It's important to watch your pet closely if it has a penchant for too much grass.

When to Contact Your Vet

Only a veterinarian can provide proper treatment for your pet, and any change in your cat's behavior warrants a visit or at least a phone call. If you suspect that your cat has eaten a significant amount of grass, or that it has consumed grass sprayed with toxic chemicals, immediately contact animal poison control and seek out your vet, or if appropriate, emergency care. Reactions to poisonous plants can range from mild to severe, and even include death. And be mindful of the plants you bring into your home, particularly bouquets and cut flowers, which are often toxic.

View Article Sources
  1. Newberry, Ruth C., and Bjarne O. Braastad (Editors). “Animal Lives Worth Living.” ISAE 2019 Proceedings of the 53rd Congress of the ISAE.

  2. Depauw, S, et al. “Animal Fibre: The Forgotten Nutrient in Strict Carnivores? First Insights in the Cheetah: Dietary Animal Fibre in the Cheetah.” Journal of Animal Physiology and Animal Nutrition, vol. 97, 2013, pp. 146-154., doi:10.1111/j.1439-0396.2011.01252.x

  3. Animal Poison Control.” American Society for the Prevention of Cruelty to Animals.