Why Cats Eat Grass

DigestiveSymptomsMeongsiljang Veterinary Advisory Board

It’s completely natural for cats to nibble on grass, as it helps them pass hairballs, aids digestion, and satisfies their instinctual urges. However, it’s essential to keep them away from toxic plants.

Why Do Cats Eat Grass?

Cats chewing on grass is an instinctive behavior that helps them pass hairballs and aids digestion. Grass is known to help swallowed fur and food move smoothly through the digestive tract. In most cases, this isn’t a sign of illness but rather a natural form of self-care. What truly matters is what they’re eating. Small amounts of safe cat grass (such as oat, wheat, or rye sprouts) are fine, but if your cat chews on indoor houseplants or toxic plants like lilies or tulips, seek veterinary care immediately. If vomiting or loss of appetite persists for more than 24 hours after eating grass, it may indicate something beyond simple instinct.

Step-by-Step Check for Grass Eating

Not all grass-eating is the same. Use the table below to distinguish between "normal range" and "signs that require a vet visit." Frequency, amount, and subsequent symptoms are the key factors for judgment.

Urgency Levels by Grass-Eating Situation

Item	Mild	Needs monitoring	See vet immediately
Frequency	1-2 times a week	Almost daily	Fixated multiple times a day
Behavior after ingestion	Same as usual	Recovers after vomiting 1-2 times	Repeated vomiting, lethargy
Plant eaten	Cat grass	Lawn grass, wild grasses	Foliage plants, lilies, tulips
Appetite	Maintained	Slightly decreased	Refusal for over 24 hours
Action	Just monitor	Identify the plant type	Go to emergency vet immediately

Lilies are extremely toxic to cats and can cause kidney failure.

Why Do They Eat It? Key Reasons Checklist

According to research in veterinary behavioral science, cats’ tendency to eat grass stems from a combination of factors. - Aiding hairball passage and gastrointestinal transit: Grass is believed to help swallowed fur and food move smoothly through the digestive tract. - Supporting digestion: The fiber in grass is thought to facilitate the movement of gastrointestinal contents, thereby aiding digestion. - Supplementing trace elements: Some explanations suggest that grass provides small amounts of trace elements to the diet. - Relieving stress: This behavior can also manifest as oral stimulation when a cat is bored or anxious. - Ancestral instinct theory (limited evidence): While some attribute this behavior to wild instincts, studies have not found a clear correlation between deworming, diet, and grass-eating.

A cat with a blade of grass in its mouth

When to Go to the Vet Immediately

If you notice any of the following signs, it may not be simple instinct but a medical emergency: ① immediate ingestion of toxic plants such as lilies, tulips, dieffenbachia, or monsteras; ② vomiting three or more times within 24 hours; ③ inability to drink water and lethargy; ④ pale gums or rapid breathing; ⑤ a sudden decrease in urine output or urine that is dark yellow. Lilies are especially highly toxic to cats—even a single leaf or a lick of pollen can lead to acute kidney failure. Even if no symptoms are present, if ingestion is suspected, seek emergency veterinary care as quickly as possible, as this will determine the prognosis.

Dangerous Plants vs. Safe Plants

Surprisingly, many plants that are easy to grow indoors are toxic to cats. - Dangerous plants: Lilies, tulips, daffodils, dieffenbachia, monstera, pothos, ivy, and aloe. - Relatively safe cat grasses: Oat grass, wheatgrass, rye grass, catnip, and cat mint. If your cat frequently nibbles on plants, it’s a good idea to review all the plants in your home. If you’re unsure about a plant’s identity, take a photo and have your veterinarian confirm it for safety.

A comparison of safe cat grass and dangerous lilies

The Relationship Between Hairballs and Grass Eating

According to veterinary internal medicine textbooks, cats swallow a significant amount of fur while grooming. When this fur accumulates in the stomach, it forms a hairball. Consuming grass is known to help the ingested fur pass through the digestive tract and be expelled. Long-haired breeds, such as Persians, Maine Coons, and Ragdolls, are particularly prone to hairballs, so it is beneficial to provide cat grass regularly. However, if your cat frequently vomits hairballs or repeatedly tries to vomit without success, you should consider hairball care food or consult a veterinarian.

How to Safely Let Cats Eat Grass

Cat grass can be purchased at pet supply stores or grown at home from seeds. - How to grow: Sprinkle oat or wheat seeds in soil, and they will grow to about 5 cm in height within 5–7 days. - Serving size: Offering 3–5 blades of grass per day is appropriate. - Pesticide caution: Never feed your cat outdoor lawn grass or garden plants, as they may be contaminated with pesticides or herbicides. - Hygiene maintenance: If mold appears on the soil surface or the leaves turn yellow, replace the pot with a fresh one. There is no need to force your cat to eat it if they show no interest.

Frequent Eating Doesn't Always Mean It's Normal

If your cat suddenly starts eating grass more often or obsessively chews on dirt, wallpaper, or plastic, it could be a sign of pica. Pica is a type of compulsive behavior disorder, often linked to early weaning stress or insufficient environmental stimulation. It’s important to first consult a veterinarian to rule out any underlying medical causes. Additionally, if your cat vomits every time after eating grass, it may indicate gastritis or inflammatory bowel disease (IBD). If you notice any unusual behavior, record a video and share it with your veterinarian.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is it okay if my cat eats grass and then vomits?

Vomiting once or twice after eating cat grass is a natural response to help expel hairballs. However, if vomiting occurs more than three times within 24 hours, or if yellow bile or blood is present, it may indicate a gastrointestinal issue, and you should take your cat to the vet.

Are there cats that don’t eat cat grass at all?

Yes, there’s a lot of individual variation. Many cats aren’t interested in grass, so there’s no need to force them to eat it. Instead, you can use hairball care food or malt paste as alternatives.

Can my pet eat the grass outside?

We don’t recommend it. There’s a risk of contamination from pesticides, herbicides, parasite eggs, dog feces, or other animals’ waste. The safest option is to offer cat grass that you’ve grown indoors.

Can I give cat grass to kittens?

You can start offering small amounts after your pet reaches 3 months of age. Since their digestive system is still sensitive, begin with just one or two leaves and monitor their reaction.

Is it dangerous even if my pet only briefly licked a lily?

Yes, it is extremely dangerous. All parts of lilies—including the pollen, leaves, stems, and even the water in the vase—are highly toxic to cats. If there is any possibility your cat has licked or ingested any part of a lily, you must take them to an emergency veterinary clinic immediately to prevent acute kidney failure.