Why Do Dogs Eat Grass? What the Research Actually Found

Published September 2026 · Pet N Pet Editorial · National Dog Day Science Series

The go-to answer is that dogs eat grass to make themselves throw up when their stomach hurts. It's repeated everywhere, and the biggest study on the subject says it's mostly wrong. In a survey of 1,571 dog owners run by veterinary researchers at UC Davis, only about 22% of dogs regularly vomited after eating grass, and only about 9% seemed ill beforehand (Sueda, Hart, and Cliff, Applied Animal Behaviour Science, 2008).

If grass were a self-prescribed vomiting aid for sick dogs, those numbers would be flipped. Instead, the picture that emerges is very different: grass-eating is a common, normal thing that healthy dogs do, the youngest and healthiest of them most of all. Here's what the research actually shows, and the honest admission at the center of it.

What the Biggest Study Actually Found

The most useful data comes from a UC Davis project that surveyed dog owners at scale. Out of 3,340 responses, 1,571 qualified for analysis, making it one of the largest looks at this behavior ever done (Sueda, Hart, and Cliff, Applied Animal Behaviour Science, 2008). The findings were consistent and clear.

About 68% of dogs ate grass or other plants daily or weekly, and among the plant-eaters, grass was by far the favorite, chosen by 79%. In a companion group where every dog had daily access to a yard, all of them had eaten grass at some point. So this isn't a quirk of a few oddball dogs. Grazing is close to universal dog behavior.

The numbers that demolish the sickness theory are the other two. Only around 9% of dogs appeared ill before they grazed, and only about 22% regularly threw up afterward. And here's the detail that really turns the theory on its head: younger dogs grazed the most and were the least likely to look sick beforehand. If grass-eating were driven by nausea, you'd expect the opposite.

The 'Upset Stomach' Myth, Tested Directly

Survey data is one thing. A controlled experiment is stronger, and one exists. Researchers in Australia deliberately gave dogs a supplement that produced a mild gastrointestinal upset, loose stools, then measured how much grass the dogs ate compared with when their digestion was normal (McKenzie, Brown, and Price, Applied Animal Behaviour Science, 2010).

If the folk theory were right, an upset stomach should have sent the dogs straight for the grass. It did the reverse. The dogs spent significantly less time eating grass when their guts were upset than when they felt fine. That's about as direct a test as you could ask for, and it points the opposite way from the myth. Dogs are not, in general, eating grass to fix a sour stomach.

So Why Do They Do It? The Honest Answer

This is the part most articles skip: we don't actually know. What the evidence rules out is that grass-eating is primarily about sickness, vomiting, or a nutritional gap, the survey found no link to any of those. What the evidence supports is that it's a normal, likely innate behavior in healthy dogs. The best current summary is genuinely "it's common, it's usually fine, and the reason is still unsettled."

The leading idea is evolutionary. Wild relatives of dogs, like wolves, do eat plant matter, and grass shows up in a meaningful share of wolf droppings. Some behaviorists, including Benjamin Hart, who co-authored the big survey, have proposed that grazing is an inherited behavior that may once have helped purge intestinal parasites. It's a reasonable hypothesis, but it hasn't been demonstrated in modern pet dogs, most of which don't carry the relevant parasites. Other explanations, boredom, the taste, simple foraging enrichment, are plausible too. None is proven.

Is Eating Grass Dangerous?

The grass itself is usually harmless for a healthy dog. The real risks aren't the blades but what's on them or near them. Lawns treated with pesticides or herbicides can make a grazing dog sick, and grass in areas used by other animals can carry intestinal parasites like roundworms and hookworms from droppings (AKC; VCA Animal Hospitals). Some ornamental and wild plants are also toxic, so a dog grazing indiscriminately in an unfamiliar area is worth watching.

In other words, the smart worry isn't "my dog ate grass," it's "what was that grass exposed to." A chemical-free yard and a dog that nibbles the occasional blade is a normal, low-risk situation. Treated grass, roadside patches, or a dog eating dirt and non-food objects along with the grass are the scenarios that deserve a second look.

When You Should Actually Call the Vet

Grazing on its own rarely needs a vet. What warrants a call is a change or a cluster of symptoms. Watch for a sudden, marked increase in how much grass your dog eats, especially if it seems frantic about it. Watch for grass-eating paired with repeated vomiting, diarrhea, lethargy, or a drop in appetite, which points to an underlying stomach or digestive problem rather than ordinary grazing (VCA Animal Hospitals).

Also flag compulsive eating of non-food items, dirt, rocks, fabric, which can be a sign of pica and deserves a check (AKC). And if there's any chance your dog got into pesticide-treated grass or a toxic plant, treat that as urgent and contact your vet or a pet poison line. Short version: occasional nibbling on a clean lawn is fine; a new, intense, or symptom-laden habit is not.

Frequently Asked Questions

Is it normal for dogs to eat grass?

Yes, very. About 68% of dogs graze on plants daily or weekly, and in one study every dog with regular yard access had eaten grass (Sueda et al., 2008). It's one of the most common behaviors in healthy dogs, and it shows up most in young, healthy animals, not sick ones, so occasional grazing is no cause for alarm.

Do dogs eat grass to make themselves throw up?

Mostly no. In the largest survey, only about 22% of dogs regularly vomited after eating grass and only ~9% seemed ill beforehand (Sueda et al., 2008). A controlled experiment even found that inducing an upset stomach made dogs eat less grass, not more (McKenzie et al., 2010). Vomiting is the exception, not the point.

Does eating grass mean my dog has an upset stomach or is sick?

Usually not. Most grazing dogs show no signs of illness first, and younger, healthy dogs graze the most. Since the data doesn't link grass-eating to sickness or nutritional gaps, an occasional nibble is best read as normal dog behavior rather than a symptom. A sudden spike paired with other symptoms is the exception worth checking.

Is eating grass bad or dangerous for my dog?

The grass itself usually isn't. The real risks are what's on it: pesticides and herbicides on treated lawns, and parasites like roundworms or hookworms in areas used by other animals (AKC; VCA). Some plants are also toxic. So a chemical-free yard is low-risk, while treated or roadside grass is what deserves caution.

When should I worry about my dog eating grass?

Call the vet if grass-eating suddenly increases a lot, if it comes with repeated vomiting, diarrhea, lethargy, or appetite loss, or if your dog compulsively eats non-food items like dirt or rocks, which can signal pica (VCA; AKC). Possible exposure to lawn chemicals or toxic plants is urgent. Occasional grazing on a clean lawn is not.

Bottom Line

Grass-eating is one of those dog behaviors we've all confidently explained and mostly gotten wrong. It isn't a self-cure for nausea, it isn't a red flag for illness, and it isn't a sign your dog's food is lacking something. It's a common, largely normal habit that healthy dogs, especially young ones, simply do, for reasons science hasn't fully pinned down. Keep the lawn free of chemicals, keep an eye out for sudden changes or added symptoms, and otherwise let your dog have its salad. Sometimes a dog eating grass is just a dog eating grass.

SOURCES & CITATIONS

Sueda, Hart, Cliff  "Characterisation of plant eating in dogs," Applied Animal Behaviour Science 111(1-2):120-132 (2008). UC Davis survey (1,571 dogs): 68% graze daily/weekly; ~9% ill before; ~22% vomit after.  https://doi.org/10.1016/j.applanim.2007.05.018

McKenzie, Brown, Price  "Reduction in grass eating behaviours in the domestic dog... in response to a mild gastrointestinal disturbance," Applied Animal Behaviour Science 123(1-2):51-55 (2010). Induced GI upset reduced grazing.  https://www.sciencedirect.com/science/article/abs/pii/S0168159109003311

Bjone, Brown, Price  "Grass eating patterns in the domestic dog," Recent Advances in Animal Nutrition in Australia (2007). Grazing tied to satiety and time of day; vomiting rare (supporting context).  https://www.une.edu.au/staff-profiles/ers/wbrown

VCA Animal Hospitals  "Why Do Dogs Eat Grass?" Notes low vomiting/illness rates and flags pesticides, herbicides, and parasites as the real risks; when to see a vet.  https://vcahospitals.com/know-your-pet/why-do-dogs-eat-grass

American Kennel Club (AKC)  "Why Does My Dog Eat Grass?" Flags compulsive non-food eating (pica), and warns treated grass and animal droppings can carry toxins and parasites.  https://www.akc.org/expert-advice/advice/why-does-my-dog-eat-grass/

Coren, S. (summarizing Hart)  "Why Dogs Eat Grass  A Myth Debunked," Psychology Today (2014). Secondary summary of the ancestral/parasite-purging hypothesis and wolf-scat context.  https://www.psychologytoday.com/us/blog/canine-corner/201412/why-dogs-eat-grass-myth-debunked