Dogs that eat grass: four common explanations

September 10, 2026

Reading time 4 min · Level 1: Why the symptom occurs

The short answer: Most dogs eat grass, and most are not unwell either before or after. The most common explanation is simply that it is normal behaviour. Dogs and wolves have always eaten plants. Only a minority vomit afterwards, and even fewer seem ill beforehand. But there are exceptions, and those are the ones you should be able to recognise.

What the research actually shows

The largest survey in the field was done at the UC Davis veterinary school. The researchers collected answers from 1,571 owners of grass-eating dogs. The result: 68 percent of the dogs ate grass daily or weekly. Only 22 percent vomited regularly afterwards, and only 9 percent seemed ill beforehand¹.

Younger dogs ate more grass than older ones, and they were less likely to seem ill beforehand or vomit afterwards. The researchers' conclusion: grass eating is normal behaviour in dogs, not primarily a sign of illness¹.

So the myth that "the dog eats grass because it wants to vomit" is true for some dogs, but not for most.

Key insight: Grass eating in itself is rarely the problem. It is grass eating together with other signs, lethargy, repeated vomiting, loose stools, changed appetite, that is worth reacting to.

Four common explanations

1. It is normal. Wild canids eat plants, and the behaviour has come along with the domestic dog. The researchers behind the UC Davis study believe it may be an inherited way of increasing gut movement and clearing out parasites, a legacy from a time when dogs had more worms than they do today². Your dog probably has no parasites, but the instinct remains.

2. It tastes good, or the dog is bored. Fresh spring grass is sweet and juicy. Many dogs graze most when the grass is at its freshest. Others do it out of habit, boredom or because they saw another dog do it. It is no stranger than us snacking without being hungry.

3. The stomach is unsettled. Here is the exception. Some dogs eat grass frantically, often coarse and long grass, and vomit shortly afterwards. If it happens once and the dog is then bright and eats as usual, let it be. If it happens repeatedly in a short time, or together with loose stools, it is a sign that the stomach really is not well.

4. The diet. There is an old idea that dogs eat grass because they lack fibre. The support is weak: in the UC Davis study the researchers saw no link between type of food and how much grass the dog ate¹. But if your dog has recently changed food and at the same time started grazing more and having looser stools, it is worth looking at the food.

The signs that mean "call the vet"

Grass eating in itself is no cause for concern. But contact a vet if the dog:

vomits repeatedly within a day, or vomits without having eaten grass
has diarrhoea lasting more than a day, or blood in the stools
is lethargic, has a painful abdomen (arches its back, does not want to be lifted) or refuses food
suddenly starts eating much more grass than usual for no clear reason

The same always applies to puppies and old dogs, they tolerate fluid loss less well.

What you can do yourself

Let the dog graze where you know the grass has not been sprayed or recently fertilised. Avoid roadsides. Do not give the dog the chance to eat large amounts of long, coarse grass, that is what most often causes vomiting.

Keep track of the pattern. Note when the dog eats grass and whether anything else happens at the same time: a food change, stress, treats from guests, what the dog found on the walk. After a couple of weeks you usually see a connection, or that there is none, and that your dog simply likes grass.

And supplements?

For the dog whose stomach is unsettled now and then, at food changes, travel or stress, many owners want to do something more alongside what the vet does. A complementary feed for the stomach is one such route. It does not treat diarrhoea and does not replace a vet in acute cases. What is in Herbiovet's DIARANNU is five herbs with a long traditional use for digestion, in stated amounts, as a short course, not as a daily supplement.