Why do cats eat grass? What the research says

Cats are carnivores, so it surprises many people to see them chewing grass like tiny cows. "Why do cats eat grass?" is one of the most common cat questions on Google, and scientists have actually studied it.

What the research found

Researchers at the University of California, Davis (Hart and colleagues) surveyed cat owners who spent time watching their cats every day. In the group of 1,021 owners:

• 71% of cats had been seen eating plants at least six times in their lives, and only about 11% had never been seen eating plants.
• In about 91% of cases, the cats appeared completely normal before eating plants: no sign of illness.
• About a quarter of cats (27%) were reported to vomit frequently afterwards.
• Young cats ate plants more often, but vomited less.

In other words, cats don't usually eat grass because they feel sick, and eating grass doesn't always make them sick.

So why do they do it?

The leading theory is that it's an inherited instinct. Wild cats swallow hair, feathers and bones with their prey, and often carry intestinal parasites. Eating grass increases muscle activity in the gut, which may help push unwanted material (and some parasites) through or out. Plant material has been found in the stomachs and droppings of wild cats too.

A related idea is the hairball hypothesis: grass may help cats bring up or pass swallowed hair. This fits with long-haired cats swallowing more hair. (Regular brushing helps too: see why brushing matters.)

And some cats probably just like the texture and taste.

How to offer grass safely

• Grow cat grass (usually wheat, oat or barley grass) in a pot indoors. It's cheap, safe and many cats love it.
• Avoid treated lawns: pesticides and fertilisers can be harmful.
• Know your plants. Many common house and garden plants are toxic to cats, some seriously (lilies, oleander, sago palm and more). See our guide to plants that can poison a cat.
• In multi-cat homes, offer more than one pot so nobody has to compete.

When to see a vet

Occasional grass-eating and the odd vomit afterwards is normal. See your vet if your cat:

• vomits often, even without eating grass (see IBD in cats)
• suddenly eats large amounts of plants, or other non-food things
• has diarrhoea, weight loss, lethargy or a poor appetite
• may have eaten a toxic plant (go immediately, and take the plant with you)