Why does my cat eat grass?
PetMD is clear that this is normal behavior, not a symptom: eating grass shows up in healthy cats all the time. The studies are thin, but veterinarians hold a few workable theories:
- Clearing the stomach — wild ancestors ate grass to help expel indigestible prey parts (feathers, small bones); modern cats may do it to clear hairballs. A 2021 study found no difference between long- and short-haired cats, so the hairball theory is unproven.
- Fiber for the gut — grass that isn't vomited usually passes through and may help mildly constipated cats.
- Parasite control — plausible evolutionarily; seen in other wild species.
- Trace nutrients — possible, but unproven in studies.
- It just tastes good — some cats genuinely like it.
Is it normal for cats to throw up after eating grass?
Yes — and PetMD explains why: cats are carnivores and can't digest fibrous grass the way cows and horses can. The grass irritates the stomach on the way through and frequently comes back up, or shows up unchanged in the stool.
The same mechanics are why the behavior may have stuck around. In the wild, vomiting grass after a meal is nature's way of clearing the parts of prey a cat can't digest (PetMD/Siracusa).
The line to watch: frequent eat-then-vomit cycles. PetMD says repeatedly vomiting grass can point to gastrointestinal disease — inflammatory bowel disease or parasites — and recommends vet testing (fecal exam, blood work, sometimes ultrasound), especially if the habit is new or getting worse.
Is grass safe for cats?
- Pesticides and fertilizer — untreated grass is safe; treated lawns are the risk. Keep cats off recently sprayed grass (PetMD).
- Long pieces and big mouthfuls — grass fibers are hard to digest, and large or very long amounts can cause an intestinal blockage. Supervise enthusiastic grazers (PetMD).
- Houseplants — indoor cats denied grass often chew plants instead, and many common houseplants are genuinely toxic. PetMD suggests growing cat grass (rye, barley, oat or wheat) so the nibbling has a safe target.
- Soil and potting material — cats who pull grass up by the roots swallow dirt too.
When to see your vet
See the vet if your cat eats grass and then vomits frequently, if the habit is new or escalating, or if it comes with weight loss, diarrhea or appetite changes (PetMD).
Also call if you suspect a blockage: repeated vomiting, straining, lethargy, or refusal to eat after a grass binge. And as PetMD's behaviorist points out, a quick word with your vet before bringing any new plants home — cat grass kits included — is always reasonable.
Frequently asked questions
Do cats eat grass when they're sick?
Sometimes — but PetMD stresses it's a myth that grass-eating means illness. Healthy cats do it too. What matters is the pattern: frequent grass-then-vomiting, or a brand-new habit, deserves a vet visit.
Why does my cat eat grass and then throw up every time?
Cats can't digest the fiber, so grass commonly comes back up (PetMD). If it's every single time — or paired with diarrhea, weight loss or lethargy — PetMD flags possible GI disease like inflammatory bowel disease or parasites worth testing for.
Should I stop my cat from eating grass?
You don't need to stop the behavior; PetMD calls it natural. Just manage the risk: keep her off treated lawns, watch for long blades, and offer indoor cat grass so houseplants stay untouched.
Is cat grass safe for indoor cats?
Yes — PetMD presents it as the safe alternative to pesticide-treated lawns and toxic houseplants. Grow rye, barley, oat or wheat, water without over-soaking (mold risk), and check with your vet before adding any plants to the house.