Why do cats eat grass, and why do some throw up?
Many cats nibble grass and other greens: a common, inborn habit, and vets do not know exactly why.
Most cats eat grass because it is a normal, inborn habit, not because they are ill. In large owner surveys, most grass eaters looked healthy beforehand and did not often vomit afterwards. Nobody knows the exact reason: perhaps to clear worms, to help digestion, or simply because they like it. A little grass is fine, but sprayed lawns and poisonous plants such as lilies are dangerous.
Usually normal. Eating a little grass now and then is normal in a healthy cat. Eating it daily or greedily, vomiting regularly, or chewing poisonous plants does need action.
What happens to the grass?
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What happens to the grass
Cats are meat eaters and cannot digest raw plants well. So the grass mostly passes through undigested. In the largest survey, among cats that often ate plants, about two in three had plant bits in their vomit and about one in three in their stool. Bringing it up and passing it can both be normal.
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What cat grass is
Cat grass is not a special species. It is young wheat, oat, barley or rye, grown indoors and ready to nibble after about 10 to 14 days. It is a different plant from catnip, which is a mint. Some products sold as barley grass turn out to be oat.
Why do cats eat grass? The likely reasons
It is a normal, inborn habit
About 7 in 10 cats; about 1 in 9 never does itMost cats eat plants, and most do not seem ill when they do. In two surveys from UC Davis, only 6 to 9 percent of cats often looked ill before eating plants. About 71 percent had been seen eating plants at least six times. The researchers see it as normal behaviour that house cats inherited from their wild ancestors, just like dogs.
How to tell- Nibbles calmly, often a few blades
- Acts and eats normally before and after
- Does not vomit, or only now and then
They like it, or it is something to do
Often named by vets; not measuredSome cats simply enjoy the taste and the chewing. They also nibble out of curiosity or play, or because they know plant bits from the stomachs of their prey. A few swallow things because, once something is at the back of the mouth, they cannot spit it out.
How to tell- Chews and swallows without fuss
- Likes to graze in the sun or on a window sill
- Tries other leaves and stems too
An indoor cat with nothing green to eat
Common in indoor catsCats that chew houseplants and flowers are usually indoor cats with little access to grass. Most cats have a steady urge to nibble plants, so an indoor cat takes what is there, even a poisonous plant. A bouquet is also something new in the home, and kittens and young cats like to chew it.
How to tell- Chews houseplants or flowers
- Goes back to the same plant
- A home without a balcony or garden
Sometimes to settle an upset stomach or bring something up
About 27 to 37 percent often vomit after; most do notMany people think cats eat grass in order to vomit. That is not proven. About a quarter to a third of cats often vomit after eating plants, and some vets see grass as self-help for nausea. But most cats do not look ill beforehand and most do not vomit. The blades can also tickle the throat or irritate the stomach and set off vomiting by themselves. Does your cat suddenly eat a lot of grass? Then keep a close eye on it.
How to tell- Eats grass fast and vomits foam or grass within minutes
- Drools, licks its lips or goes off its food (then it may be ill)
Perhaps to clear gut worms (an idea, not proven)
The explanation researchers name most, but untestedThe UC Davis researchers think wild meat eaters keep gut worms in check by eating plants regularly. Grass is not digested and may get the gut moving, so worms are pushed out with it. This has not been tested. It would explain why young cats eat more plants: they cope less well with parasites. In a small Vienna study, outdoor cats that were dewormed more often ate less grass.
How to tell- A calm, regular habit, not a sudden craving
- More common in young cats and outdoor cats
Fibre and hairballs (weak evidence)
Often repeated, not provenYou often read that grass is fibre that helps digestion and clears hairballs. The evidence is weak. Short-haired and long-haired cats eat plants equally often, which does not fit a hairball reason. A very small 2025 study found plant fibres tangled in hair, so grass may catch hair in some cats. Nobody has shown that grass reduces hairballs.
How to tell- Hair comes up with the grass
Missing nutrients (unproven, probably rare)
Not measuredSome sites say grass gives cats folic acid, vitamins or chlorophyll. No study in cats shows this. Cats are meat eaters and a complete cat food covers their needs. So do not give a supplement without asking the vet. Does your cat eat a lot of grass or want nothing else? Then do have its diet checked.
How to tell- Eats a lot of grass and little of its own food
- A new, strong craving for plants
Sometimes stress or boredom
UnclearAccording to one vet, constantly chewing grass or plants can be a way of coping with stress. An indoor cat with little to do may also chew out of boredom. Does your cat chew non-stop, and do you see other changes, such as hiding, grooming a lot or peeing outside the litter box? Then have it checked first, and after that look at its day, play and hiding places.
How to tell- Chews plants for long or many times a day
- Other changes in behaviour too
Eating grass and throwing up, plants and flowers
- Grazing on the lawn or in the garden
- This is the classic picture, and it is usually harmless. The danger is not the grass but what is on it: weedkiller, fertiliser, slug pellets and droppings. A cat that grazes down to the roots can also pick up worm eggs from the soil. Keep it off treated lawns and offer cat grass at home as a clean choice.
- Your cat eats grass and then throws up right away
- About a third of grass eaters do this often, and in an otherwise healthy cat it is usually normal. The blades irritate the throat and stomach, or hair or food comes up with them. If it happens now and then and your cat is bright, eats and drinks, you can watch. If it happens every time, or once a week or more, have it checked.
- Your cat eats grass without vomiting
- Most grass eaters do not vomit. The grass passes along with the food and ends up in the stool. That is normal.
- Your indoor cat eats your plants
- Indoor cats often go for houseplants. Look up every plant by its exact name, move poisonous ones out of reach or out of the home, and give your cat its own pot of cat grass. Cat grass alone will not keep it off other plants, so poisonous ones must be truly out of reach.
- Your cat sniffs or chews a bunch of flowers
- Check a bouquet before it comes in. Lilies often hide in mixed bouquets, and for a cat pollen on the fur or vase water is already enough. Safe cut flowers include roses, sunflowers, orchids, zinnias and gerberas.
- Gagging, sneezing or coughing after grass
- A grass blade or seed can get stuck at the back of the nose or throat, or in an ear, eye or paw. Heavy sneezing, gagging, retching and not wanting to eat are the signs. Only removing it helps, and a vet may need to sedate your cat to do it.
- Your cat suddenly eats much more grass
- Does your cat suddenly eat large amounts, or want only grass and not its usual food? That can point to a digestive problem or a diet that falls short. See the vet.
- Your cat eats the potting soil too
- Some cats eat the soil along with the grass, which can give them diarrhoea. Watch what your cat does with the pot, and throw a pot out once it turns mouldy.
Cat grass and plants: how to keep it safe
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Let a healthy cat nibble a little grass. Do not punish it, and do not force it either.
Eating grass is natural and safe in itself. The danger lies in what is on the grass and in poisonous plants.
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Give an indoor cat its own cat grass: oat, wheat, barley or rye, as a ready pot or grown from seed.
It gives your cat something safe to chew, without the chemicals that may be on outdoor grass, and may keep it off your houseplants.
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Sow it in a shallow pot with drainage: soak the seeds overnight, sow in damp soil, keep it bright and lightly watered. It is ready after 10 to 14 days. Put the pot where your cat likes to sit, such as the window sill, and start a new pot every few weeks.
Young grass is soft. Too much water breeds mould, and mouldy cat grass upsets the stomach. A pot in its own spot is more likely to feel like your cat's own.
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Offer a little at a time, and take the pot away after a few bites if your cat gobbles it.
A lot of grass in a short time makes cats vomit, and what does not come up can build up in the gut.
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Look up every houseplant and bouquet by its exact name. Remove poisonous plants, never bring lilies home, and put anything doubtful out of reach.
A cat cannot tell safe grass from a poisonous plant, and some plants are deadly in very small amounts.
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Keep your cat off lawns that may be treated with weedkiller, fertiliser or slug pellets, and ask what neighbours or the landlord use.
Those chemicals can be very harmful, and outdoor grass may also carry worm eggs.
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Has your cat vomited once and is it otherwise bright? Offer a little fresh water, watch it closely and give small meals later. Call the vet if it vomits again or seems unwell.
One vomit after grass in a healthy cat is often nothing. Vomiting again and again is not.
Better not
- Do not keep lilies in the home, in a vase or in a garden your cat can reach, and do not wait to see if it gets ill after touching one.Every part of a true lily and a daylily is poisonous, including pollen and vase water, and it can lead to kidney failure and death.
- Do not let your cat eat grass treated with weedkiller, fertiliser or pesticides.These can be very harmful, and your cat swallows them as it grazes.
- Do not assume a plant is safe because it looks like one you know, or because your cat is used to cat grass.Whether a plant is poisonous depends on the exact species. And a cat used to grass may think all greens are safe, such as rhododendron or tiger lily.
- Do not count on sprays, hot sauce or tricks to protect poisonous plants.The only sure protection is making sure your cat truly cannot reach them.
- Do not offer large amounts of grass, mouldy cat grass or stiff, sharp grass.Too much makes a cat vomit or builds up in the gut, and mould can be toxic. Hard blades can scratch the mouth and get stuck in the throat or nose.
When to see a vet?
Eating grass is not in itself a reason to see the vet, and the odd vomit after grass in a bright cat is usually nothing. Do go soon if your cat vomits regularly, seems unwell or eats grass in large amounts. Could it have eaten a poisonous plant, especially a lily? Then it is an emergency: call your own vet or the emergency vet at once. This page does not diagnose; the vet does.
- Emergency, now: your cat has chewed, licked or drunk from any part of a lily, even just pollen on its fur. Call the vet at once and do not wait for signs.
- Emergency, now: your cat has eaten any part of a sago palm, oleander or autumn crocus, or you do not know which plant it was. Call a vet or emergency vet at once.
- Same day: vomiting for more than 24 hours or again and again, or not keeping food or water down.
- Same day: blood or black specks in the vomit, retching with nothing coming up, a swollen or painful belly, pale or yellow gums, weakness, diarrhoea, or drinking and peeing much more.
- Same day: lots of sneezing, gagging or retching after grass, or not wanting to eat (a blade may be stuck in the nose or throat).
- Soon: a very young or old cat that vomits.
- Soon: vomiting after grass every time, or once a week or more.
- Soon: eating grass daily or many times a day, suddenly a lot, or wanting only grass.
- At the check-up: vomiting more often, also without grass, or with changes in weight, appetite, energy or stool.
What research says
Most cats are not ill when they eat plants
In two surveys, only 6 and 9 percent of cats often looked ill before eating plants, while 27 to 37 percent often vomited afterwards. In the second survey, 91 percent acted normally beforehand.
Hart, Hart, Thigpen and Willits, UC Davis, 2021Plant eating is very common, and kittens do it most
Of 1,021 cats, 71 percent had been seen eating plants at least six times, and 11 percent never. Of cats under one year, 93 percent ate plants weekly, against 58 percent of cats over nine years.
Hart, Hart and Thigpen, UC Davis, 2019Long-haired cats do not eat more grass, older cats vomit more after it
Short-haired and long-haired cats ate plants equally often, so hairballs do not explain it. Vomiting after plants rose with age: from 2.7 percent under one year to 57 percent over nine years.
Hart, Hart, Thigpen and Willits, UC Davis, 2021Plant fibres may catch hair, but the study is tiny
Under the microscope, six hairballs from two cats had plant fibres tangled in the hair. Grass may catch hair in some cats, but this does not show that grass reduces hairballs.
Researchers at High Point University, 2025Wild cats eat some plants too
In feral cats, about 12 percent of stool or stomach samples held plant material. In a small Vienna study of 97 cats, outdoor cats that were dewormed more often ate grass less often. This is early, small-scale evidence.
Review of plant-eating carnivores; Novak, Vetmeduni Vienna, 2024
Story or true?
A cat that eats grass is ill.
No. Most grass eaters look healthy before and after. Only a small share look ill first.
Cats eat grass to make themselves vomit.
Not proven. Many cats eat grass without vomiting, and there is no solid evidence that they do it in order to vomit.
Long-haired cats eat grass to get rid of hairballs.
Short-haired cats eat plants as often as long-haired cats, so surveys do not back this. A small study found fibres in hair, but that is far from proof.
Cats eat grass for folic acid or vitamins.
No study in cats shows this. Cats are meat eaters, and a complete cat food covers their needs.
Cat grass and catnip are the same.
No. Cat grass is young wheat, oat, barley or rye. Catnip is a mint.
Grass is dangerous for cats.
Grass itself is safe. The risks are treated lawns, long stiff blades and seeds, poisonous plants and too much at once.
Did you know?
- 7 in 10
About 71 percent of cats in a UC Davis survey had been seen eating plants at least six times. 11 percent never.
- 6%
In the two surveys, only 6 to 9 percent of cats looked ill before eating plants.
- 93%
93 percent of cats under one year ate plants weekly, against 58 percent of cats over nine years.
- 12%
About 12 percent of stool or stomach samples from feral cats held plant material.
- 10 to 14 days
Cat grass is ready to nibble 10 to 14 days after sowing, and lasts one to three weeks.
- 36 to 72 hours
After a cat chews a lily, kidney failure can follow within about 36 to 72 hours if it is not treated.
Kittens and older cats
- Kitten
Kittens eat the most plants: 93 percent of cats under one year ate plants weekly, and more often other greens than grass. Only about 3 percent vomited after. Young cats also easily chew poisonous plants and bouquets, so keep lilies and other dangerous plants out of reach and offer cat grass from the start. A kitten that vomits again and again needs a vet.
- Older cat
Older cats eat less grass but vomit after it more: in one survey, 57 percent of cats over nine years often vomited after plants. If an older cat suddenly eats a lot of grass or vomits regularly, see the vet. A very old cat that vomits should be seen sooner.
Frequently asked questions
Why do cats eat grass and then throw up?
About a quarter to a third of grass eaters often vomit afterwards. The blades tickle the throat or irritate the stomach, or hair or food comes up with them. Most cats do not vomit. Now and then is usually fine in a bright cat; every time, or once a week or more, is a reason to see the vet.
Why do cats eat cat grass?
Cat grass is just young oat, wheat, barley or rye. Cats eat it for the same reasons as lawn grass: it is a normal habit, and many like the taste and the chew. Indoors it is the safe place for that habit, away from chemicals and poisonous plants.
Why does my cat eat my plants or flowers?
Most cats have a steady urge to chew plants, and an indoor cat only has what is in the home. A new bouquet or plant is also exciting. Give it its own cat grass, look up every plant, never bring lilies home and move poisonous plants out of reach. Does it chew non-stop? Then ask the vet about stress and health.
Which flowers and plants are poisonous to cats?
Lilies are the most dangerous: a little pollen or vase water can cause fatal kidney failure. Sago palm, oleander and autumn crocus are deadly too. Azalea, tulip bulbs, dieffenbachia, philodendron, ivy and aloe vera make cats ill. Always look a plant up by its exact name.
Should I stop my cat eating grass?
No, a healthy cat can eat a little untreated grass. Only stop it if the grass has been sprayed, if your cat eats a lot or vomits every time, or if poisonous plants are close by. Cat grass indoors is a good alternative.
How much cat grass can a cat eat?
A little at a time. Put the pot down and take it away after a few bites if your cat gobbles it. Treat grass as a treat: together with other treats, no more than about 10 percent of the day's calories. Too much can cause vomiting or build up in the gut.
Why do cats and dogs eat grass?
Dogs do it too, probably for similar reasons. Cats do it somewhat less often, perhaps because their ancestors had fewer worms or because cats bury their stool. The researchers think it is an old, inborn habit in both.
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