Why Does My Dog Eat Grass Then Throw Up?

It's Extremely Common

If your dog eats grass, you're not dealing with anything unusual. Studies suggest that somewhere around 70 to 80 percent of dogs eat grass at least occasionally. It's one of the most common behaviours that sends pet owners to Google, and understandably so — watching your dog graze like a small cow and then throw up on the carpet is not a reassuring sight.

But here's the reassuring part: veterinary researchers have looked into this quite extensively, and the overwhelming consensus is that grass eating in dogs is normal behaviour, not a symptom of disease.

The Theories

Nobody has pinned down a single definitive reason why dogs eat grass. There are several plausible explanations, and the truth is probably that different dogs do it for different reasons.

They just like it. This is the simplest explanation and probably the most common one. Dogs are opportunistic eaters with wide-ranging tastes. Some dogs clearly seek out specific types of grass — they'll walk past one patch to nibble on another. Young grass shoots in spring seem to be particularly popular. If your dog eats grass casually while on a walk, tail wagging, showing no signs of distress, they're probably just enjoying a snack.

Mild stomach discomfort. Some dogs seem to eat grass specifically when their stomach is bothering them. The behaviour looks different — they'll be restless, licking their lips, swallowing repeatedly, and then urgently seeking out grass. They tend to eat it quickly and without much chewing, and they're more likely to vomit afterwards. The long, unchewed blades of grass may tickle the throat or stomach lining and trigger the vomiting reflex.

Whether this is a deliberate, self-medicating behaviour is debated. Some veterinary researchers think dogs have learned that eating grass can help them bring up something that's bothering their stomach. Others think the stomach discomfort and the grass eating are just coincidental — the dog feels off, eats grass because it's available, and vomits because it was already going to.

Dietary instinct. Dogs are not strict carnivores. Their wild ancestors ate entire prey animals, including the stomach contents of herbivores, which would have been full of plant material. Some researchers suggest that an occasional desire to eat plant matter is a vestige of this ancestral diet. Grass is readily available plant fibre, and some dogs may seek it out instinctively.

Boredom or anxiety. Dogs that spend long hours in a garden without much stimulation sometimes develop habitual grass eating. It gives them something to do. This is more likely if the grass eating is frequent, prolonged, and happens mainly when the dog is alone.

The Vomiting Part

Here's what surprises most people: the majority of dogs who eat grass don't vomit. A study published in the journal Applied Animal Behaviour Science found that only about 22% of dogs frequently vomited after eating grass, and only 9% frequently appeared ill beforehand.

When dogs do vomit after eating grass, it's often because they've eaten it quickly without chewing. Long blades of grass can irritate the stomach lining or tickle the back of the throat. It's mechanical rather than toxic — the grass itself isn't making them sick.

If your dog eats grass gently and keeps it down, there's almost certainly nothing to worry about. If your dog frantically eats grass and then vomits, pay attention to how often it happens but don't panic over isolated incidents.

When Should You Actually Worry?

Most grass eating is benign. But there are situations where it's worth mentioning to your vet:

Sudden change in behaviour. If your dog has never been much of a grass eater and suddenly starts eating it compulsively, something may have changed. This could be a dietary issue, gastrointestinal discomfort, or even nausea from an unrelated condition.

Frequent vomiting. Occasional vomiting after grass eating is normal. Vomiting multiple times a week, whether grass is involved or not, is worth investigating.

Other symptoms alongside the grass eating. If your dog is also lethargic, has diarrhoea, is losing weight, refusing food, or showing any other signs of illness, the grass eating may be a response to an underlying problem rather than a standalone behaviour.

Obsessive grass eating. If your dog eats grass constantly and can't seem to stop, it could be a compulsive behaviour or it could indicate a nutritional deficiency. Some vets suggest adding more fibre to the diet to see if the behaviour reduces.

One Genuine Concern: Pesticides and Herbicides

The grass itself isn't toxic to dogs. But what's on the grass might be. Lawns treated with pesticides, herbicides, or fertilisers can be genuinely harmful. This is the one practical reason to discourage grass eating, at least in certain locations.

Be cautious about:

• Freshly treated lawns (your own or in public spaces)
• Golf courses and manicured public gardens that are likely chemically maintained
• Verges near busy roads where runoff may concentrate chemicals

Your own untreated lawn or a meadow on a country walk? Generally fine.

What You Can Do

Like understanding why cats purr (it is not always because they are happy), interpreting your dog's grass eating requires looking at the full context rather than assuming one explanation.

If the grass eating doesn't bother your dog, it doesn't need to bother you. But if you'd like to reduce it:

• Make sure your dog is on a complete, balanced diet appropriate for their age and size
• Try adding a small amount of steamed vegetables (green beans, broccoli, or spinach) to their food — this provides plant matter in a controlled way
• Ensure your dog gets enough physical and mental stimulation, especially if they spend time alone in the garden
• If you think the grass eating is linked to stomach discomfort, keep a log of when it happens and what your dog ate in the hours before — patterns may emerge

Related: Why Do Cats Purr? · How to Get Rid of Ants Without Killing Them · Why Do Paper Cuts Hurt So Much?