Why Does My Cat Eat Grass? The Science Behind It

Reviewed by Dr. Ameer Hamza, DVM

Watching a cat methodically chew on grass and then sometimes vomit it back up is one of the stranger sights in everyday cat ownership. It looks odd, but it is entirely normal. Grass eating is a widespread behaviour in domestic cats and their wild relatives, and researchers have proposed several plausible explanations for why cats do it. This guide covers what we know about the behaviour, whether it is safe, and how to provide appropriate plant material for indoor cats.

How Common Is Grass Eating in Cats?

More common than most owners realise. A survey study published in the journal Ecology and Evolution found that 71% of cats were observed eating grass on at least 10% of observed occasions, and that 91% of cats ate plants at some point. The behaviour was not associated with signs of illness — most grass-eating cats appeared perfectly healthy before and after. Grass eating has also been documented in wild felids including lions, leopards, and cheetahs, suggesting it is an ancestral behaviour rather than a quirk of domestic cat feeding.

Proposed Explanations for Grass Eating

Parasite expulsion. The most compelling evolutionary theory is that grass eating serves to expel intestinal parasites. Grass irritates the gastrointestinal tract and increases muscle contractions. In wild cats that regularly consume whole prey — bones, fur, feathers, and any parasites the prey hosted — periodic grass eating may help purge indigestible material and worm burdens. Domestic cats do not typically have worm burdens of the same magnitude, but the behaviour may persist as an ancestral reflex.

Hairball management. Cats ingest large amounts of hair through normal grooming. Grass may help move hairballs through the digestive tract or stimulate vomiting that expels them. However, the research survey noted above found that only about 27% of grass-eating cats vomited afterwards, making hairball expulsion an incomplete explanation for the behaviour.

Nutritional supplementation. Plant material, including grass, contains folic acid and other micronutrients. Some researchers have suggested cats may seek out grass as a folic acid source. However, complete commercial cat foods are nutritionally balanced for cats, so this explanation is stronger for wild cats on exclusive meat diets.

Instinctual behaviour. The simplest explanation — sometimes the correct one — is that the behaviour is an instinctual reflex that persists in domestic cats even without the specific pressures (parasites, incomplete prey digestion) that originally selected for it. Many feline behaviours fall into this category.

Is Grass Eating Safe?

Eating grass itself is safe for cats, with one significant caveat: pesticides and herbicides. Grass treated with lawn chemicals, weed killers, or fertilisers is not safe for cats to eat. If your cat has access to a garden or outdoor areas, be aware of what has been applied to the grass. Grass that appears to have been recently treated, or that comes from communal areas where pesticide use is possible, should be considered unsafe for grazing.

The act of grass eating and subsequent vomiting is not harmful unless the vomiting is frequent, prolonged, or accompanied by other signs of illness. Occasional vomiting of grass material is normal. If vomiting is occurring more than once or twice weekly regardless of grass access, a vet consultation is appropriate.

Toxic Plants: The Real Concern

The behaviour of plant chewing is not in itself dangerous, but the plant being chewed absolutely can be. A number of very common houseplants are highly toxic to cats. The most dangerous include: lilies of any species (Lilium and Hemerocallis — all parts of true lilies are nephrotoxic to cats, and even small ingestions cause acute kidney failure); pothos (causes oral and GI irritation); peace lily (oral and GI irritation, not a true lily but marketed as one); oleander (cardiac toxicity); sago palm (severe liver toxicity); azalea and rhododendron (cardiovascular toxicity). Any cat that has eaten a lily must be treated as a veterinary emergency regardless of whether symptoms have appeared yet. Check every houseplant in your home against a reliable cat-toxic plant list and remove any that pose a risk.

Cat Grass for Indoor Cats

Indoor cats that show interest in plant chewing can be given cat grass as a safe, appropriate outlet. Cat grass is typically wheatgrass, oat grass, barley grass, or a seed mix sold specifically for cats. It grows quickly from seed and can be replaced regularly to keep it fresh. Growing your own ensures it is free of pesticides. Cat grass pots are widely available pre-grown in pet shops and supermarkets. Place it near where your cat likes to spend time. Most cats investigate and use it readily, particularly if they have shown interest in other plant material. This also has the practical benefit of redirecting plant-chewing behaviour away from any unsafe houseplants.

When Grass Eating Warrants a Vet Visit

Occasional grass eating in a healthy cat is normal and no cause for concern. Worth investigating with a vet if: grass eating has suddenly increased significantly without explanation; the cat is vomiting frequently (not just after grass ingestion); the cat appears to be chewing compulsively on non-food materials (pica); or the grass eating is accompanied by other signs like reduced appetite, weight loss, or changes in stool. Compulsive plant eating in particular can indicate gastrointestinal disease, nutritional deficiency, or stress-related behaviour in some cats.

Frequently Asked Questions

Is it normal for cats to eat grass?

Yes — studies find the majority of cats eat grass at least occasionally. It is widespread in both domestic and wild cats and is not a sign of illness.

Does eating grass make cats vomit intentionally?

Only a minority of grass-eating cats vomit afterwards. The behaviour does not appear to be primarily driven by a desire to vomit. It may have multiple functions including parasite expulsion and hairball management.

Can grass eating indicate a health problem?

Occasional grass eating in a healthy cat — no. A sudden increase in grass eating, compulsive plant chewing (pica), or accompanying signs of illness warrant a vet visit.

What grass is safe for cats?

Wheatgrass, oat grass, and barley grass grown specifically for cats are safe. Outdoor grass is safe if untreated with pesticides or herbicides. Avoid any lawn chemicals near areas your cat grazes.

Should I stop my cat from eating grass?

No — if the grass is safe. Redirect plant-chewing behaviour to safe cat grass to keep them away from toxic houseplants.

For a full overview of cat health and nutrition, see the complete cat care guide.

---

Disclaimer: This article is for educational purposes only. If your cat has eaten a potentially toxic plant, contact a veterinarian immediately — do not wait for symptoms to appear.