Reviewed by Dr. Muhammad Usman, DVM, RVMP, Pakistan- and Qatar-licensed Veterinarian
Diarrhea is an extremely frequent gastrointestinal disorder for which many canine patients will suffer. While an isolated episode of loose stools may have been triggered by an easily correctable problem (eating table scraps, rapid change from old to new food), episodes of persistent, severe, or blood-tinged diarrhea are often signs of parasitic infections; bacterial infections; chemical toxins; swallowed objects obstructing the GI tract; acute pancreatitis; etc.
There is no reason to presume that each episode of diarrhea has the same cause. Diarrhea is simply a symptom, and the proper course of action for treating diarrhea depends on what is causing it. (Merck Veterinary Manual)
What Is Diarrhea in Dogs?
Normal stool formation occurs when the digestive tract functions properly to absorb nutrients, water, and electrolytes from food. Diarrhea results when the process of digestion fails or is disrupted, resulting in soft, frequent, more watery, or larger volumes than normal stools.
Diarrhea can be caused by several mechanisms. The small intestine may secrete excessive fluid. The small intestine may not absorb nutrients and water properly. The small intestine or large intestine may become inflamed. The small intestine or large intestine may move its contents too quickly for adequate absorption. Oftentimes more than one mechanism causes the problem. (Merck Veterinary Manual)
The pattern of Diarrhea may provide useful clues as to which system of the gastrointestinal tract is involved. For example, dogs with large-intestinal diarrhea may have frequent, urgent defections; they may pass small amounts of stool with mucus or fresh blood. Small-intestinal diarrhea tends to produce larger quantities of stool, and it may also be associated with weight loss, poor nutrient absorption, etc.
Why Does My Dog Have Diarrhea?
There are many possible causes. Some are temporary and relatively mild, while others require prompt veterinary attention.
1. Eating Something They Shouldn’t
Dietary indiscretion is probably one of the most familiar causes of sudden diarrhea in dogs.
Dogs may eat:
- Garbage
- Spoiled food
- Fatty foods
- Table scraps
- Animal feces
- Plants
- Unfamiliar treats
- Food found outdoors
A sudden diet imbalance or irritant consumed can be harmful to the intestines and produce an acute case of diarrhea. According to veterinary literature, “dietary indiscretion” and other feed-related disorders are among the main reasons for gastrointestinal illness in dogs.
If you believe that your dog is otherwise healthy, is still able to drink water, and is experiencing only a minor episode of diarrhea, then it is likely that the issue will resolve itself as long as your pet receives proper support. On the other hand, if you have reason to believe that your dog has eaten a toxic substance or has swallowed a possibly hazardous item from its environment, then you should consult with a veterinarian.
2. Sudden Food Changes
Changing your dog’s food quickly may affect their digestive system. The intestinal microbiome (the bacteria that live inside the intestines) and digestive system adjust to what you are feeding your dog on a daily basis. When you change your dog from eating one food to another food, introduce many different treats, or drastically increase how much you give your dog each day, it will most likely cause gastrointestinal upset. A gradual change in dog food is usually better than making the change all at once, especially if your dog has a sensitive digestive system.
3. Food Intolerance or Food Allergy
Some dogs will have GI symptoms when they eat certain things. A dog could develop a food intolerance to an ingredient in its food, which would cause digestive issues but is not a classic allergic reaction.
An allergic reaction to food could also lead to GI or skin problems in some dogs. If diarrhea continues to occur after eating a specific food for you and your vet, it is possible she/he could suggest you perform an elimination/therapeutic diet trial instead of just picking new foods at random. The Merck Veterinary Manual states that if done correctly, a dietary trial can be one method to evaluate and manage chronic intestinal disease. (Merck Veterinary Manual)
4. Intestinal Parasites
Parasites are another important cause of diarrhea, particularly in puppies and dogs that have exposure to contaminated soil, feces, water, kennels, dog parks, or other animals.
Potential intestinal parasites include:
- Giardia
- Roundworms
- Hookworms
- Whipworms
- Coccidia
Dogs with giardiasis often experience diarrhea, which could be acute, chronic, or episodic. The stool of such animals may appear to include mucus as well as possibly being quite malodorous. However, many dogs do not display symptoms that would indicate they were infected by this organism. (Companion Animal Parasite Council)
Parasites may occasionally be present in low numbers at different times, so a single fecal examination may not identify all instances of an infection. Depending on the specific case, veterinarians may employ one of several techniques to test for Giardia; these tests include fecal flotation, antigen testing, microscopic examinations, or polymerase chain reaction (PCR)-based testing.
Additionally, the Companion Animal Parasite Council suggests using parasite testing on dogs showing symptoms consistent with a parasite infection and lists numerous methods for detecting Giardia.
5. Viral Infections
Viruses may also produce diarrhea. Diarrhea caused by viruses can include vomiting; decreased food intake; elevated temperature; weakness; or dehydration.
Of particular concern for puppies and unvaccinated dogs are viral infections resulting in severe symptoms including, but not limited to, vomiting, bloody diarrhea, severe dehydration, and systemic disease.
Prompt examination is recommended when a dog has signs consistent with Parvo virus since both water loss and electrolyte imbalance will progress rapidly if left untreated. According to the Merck Veterinary Manual, supportive care and hydration are key components of therapy for dogs infected with Parvovirus. Those experiencing severe symptoms require IV fluids.
6. Bacterial Gastrointestinal Infections
Diarrhea and Intestinal Inflammation Caused by Bacteria. Some types of bacteria can cause diarrhea and intestinal inflammation in dogs.
The presence of bacteria in a dog’s gastrointestinal system is not always an indication to treat with antibiotics. Dogs are normally colonized with multiple strains of bacteria within their intestines. Many conditions may lead to diarrhea in addition to bacterial infections.
The current WSAVA/ENOVAT guidelines state that the majority of acute canine diarrhea treated by veterinarians will be relatively mild and will respond well to supportive treatments. Most (if not all) instances of mild to moderate acute canine diarrhea do not warrant the use of antimicrobials; however, the inappropriate administration of antibiotics could result in a disruption of the normal balance of bacteria in the intestines as well as contribute to the development of resistant strains of bacteria. (wsava.org)
This is why pet owners should not give leftover antibiotics to a dog with diarrhea unless specifically instructed by a veterinarian.
7. Stress and Anxiety
Stress can affect the gastrointestinal tract.
Some dogs develop loose stools after events such as:
- Boarding
- Travel
- Moving house
- Visits to the veterinary clinic
- Introduction of another pet
- Changes in household routine
- Separation from their owner
Stress-related diarrhea is often temporary, but recurring episodes should not automatically be attributed to anxiety. Persistent diarrhea warrants investigation for other causes.
8. Foreign-Body Ingestion
Dogs are notorious for swallowing objects they should not eat.
Examples include:
- Toys
- Socks
- Bones
- Stones
- Fabric
- Plastic
- Corn cobs
A foreign object may produce a partial or total blockage of the gastrointestinal tract.
Diarrhea will never exclude the possibility of obstruction. The initial symptoms of a dog with an obstruction are often diarrhea or vomiting before it develops into a serious condition.
The dog’s owner needs to become aware if their dog is experiencing abdominal pain; repeatedly vomiting; showing no interest in food (anorexia); experiencing increased pressure on its abdomen (distended abdomen); having excessive fatigue; and/or being unable to pass feces. Gastrointestinal obstruction is potentially fatal. It may require X-rays or other forms of imaging, as well as surgical intervention.
9. Pancreatitis
Pancreatitis, or inflammation of the pancreas, can cause gastrointestinal signs including vomiting and diarrhea.
Some dogs may also develop:
- Abdominal pain
- Loss of appetite
- Lethargy
- Dehydration
Fatty meals can be associated with gastrointestinal upset and may contribute to pancreatitis in susceptible dogs. A dog with persistent vomiting, abdominal pain, marked lethargy, or diarrhea should be assessed by a veterinarian rather than treated at home based only on the stool appearance.
10. Chronic Intestinal Disease
If your dog’s diarrhea persists for several weeks or keeps coming back, there could be an underlying issue that doesn’t involve just a short-term stomach problem.
Chronic enteropathy, inflammatory bowel disease, food-responsive disease, parasitic infections of the intestines, pancreatitis, malabsorption, and various forms of GI disease are some possible causes.
According to the Merck Veterinary Manual, to diagnose the type of chronic intestinal disease, it may be necessary to perform blood work, fecal examinations, radiographs, diet trials, endoscopy, and sometimes intestinal biopsies.
11. Other Medical Problems
Sometimes dogs develop gastrointestinal problems due to disease processes that occur elsewhere in the body. Examples of these types of problems include liver, kidney, pancreatic disorders, and certain endocrine and metabolic diseases. For example, if you suspect your dog has Addison’s disease and your dog is experiencing diarrhea and vomiting, you may need to take your dog to see his veterinarian for a diagnosis.
Therefore, it is not always appropriate to treat recurring diarrhea as simply being caused by a “sensitive stomach.
What Should I Do If My Dog Has Diarrhea?
The first thing you need to do is assess your dog as a whole rather than simply the stool he produces.
If your dog’s diarrhea is mild but still alert, eating comfortably, interested in his food, and drinking enough, your veterinarian will likely tell you it’s acceptable to follow some conservative treatment plans.
Depending on the dog and what is causing the diarrhea, your veterinarian may advise you to provide supportive care including feeding an appropriate gastrointestinal diet, providing adequate fluids, and monitoring your dog.
Veterinarians are now being advised by organizations such as Merck to move toward not withholding all of a dog’s nutrition when they have a gastrointestinal issue. Merck states that early nutritional intervention may lead to better recovery rates and functioning of the GI tract in many cases of canine gastrointestinal disease.
Do not force your dog to eat or drink if he is vomiting every time you attempt it and appears very ill.
Should I Give My Dog Medicine for Diarrhea?
Do not give a dog human anti-diarrheals or other medications before consulting your veterinarian.
Medications may be harmful to certain breeds of dogs, as well as older or dehydrated dogs; they could also interact adversely with their pre-existing conditions. Diarrhea is just a symptom – it does not cure the cause of the issue.
Depending on the underlying diagnosis, your veterinarian will use diet, fluids, anthelmintics (anti-parasitics), anti-emetics, etc. in treating your pet. Merck states that, if possible, treatment for an animal’s illness should focus on resolving the cause of the issue, with supportive care provided when needed.
What About Antibiotics?
Antibiotics are not always needed for diarrhea. Current WSAVA/ENOVAT acute diarrhea guidelines clearly indicate that antimicrobials are not required for mild to moderately symptomatic patients and support antibiotic stewardship. Antimicrobial treatment is recommended for dogs showing evidence of systemic disease.
When Is Dog Diarrhea an Emergency?
Seek veterinary care promptly if your dog has diarrhea accompanied by:
- Significant lethargy or weakness
- Repeated vomiting
- Blood in the stool
- Black or tarry stool
- Severe abdominal pain
- Loss of appetite
- Difficulty standing or walking
- Signs of dehydration
- Pale gums
- Abdominal swelling
- Suspected poisoning
- Suspected foreign-body ingestion
- Multiple episodes of watery diarrhea
- Rapid deterioration
Dogs such as puppies, older dogs, small breeds, and those with pre-existing medical conditions will rapidly lose body fluids due to diarrhea.
Veterinary consultation is indicated for several episodes of loose/watery stools, presence of blood in the stool, lack of appetite, lethargy, and emergency consultation if the dog shows signs of severe illness, including inability to stand or walk. (Vca)
Additionally, sudden onset of large amounts of bloody diarrhea accompanied by vomiting has been associated with acute hemorrhagic diarrhea syndrome (AHDS), which may result in significant fluid loss; intravenous fluid therapy may be warranted immediately.
How Do Veterinarians Diagnose the Cause of Diarrhea?
Your veterinarian will usually begin with a detailed history and physical examination.
Useful information includes:
- When the diarrhea started
- How frequently the dog is defecating
- Stool color and consistency
- Whether blood or mucus is present
- Recent diet changes
- New treats or foods
- Possible garbage ingestion
- Recent travel
- Contact with other dogs
- Deworming history
- Vaccination status
- Current medications
- Vomiting or abdominal pain
- Changes in appetite or water consumption
Depending on the severity and duration, testing may include fecal examination, blood tests, urinalysis, abdominal X-rays, ultrasound, or other diagnostic procedures.
For suspected Giardia, CAPC recommends combining appropriate fecal diagnostic methods because intermittent shedding can make diagnosis challenging. (Companion Animal Parasite Council)
Can You Prevent Diarrhea in Dogs?
- While you may not always be able to keep it from happening, there are ways to make sure that it doesn’t happen as often.
- Feed a Consistent and proper amount of food for the size of your dog
- Limit how many times you change your dog’s diet and give him too many treats.
- Remove hazardous materials & waste
- Stop your dog from eating spoiled foods or medications, chemicals, poisonous plants, and anything else that could be dangerous to your pet.
- Protect against parasites
- Based on the type of parasites that exist in your area and recommendations by your veterinarian, provide your dog with a parasite prevention program.
- Ensure all of your dog’s vaccines are up to date
- The most common way to protect against parvo virus and other serious infections, which can lead to death, is through vaccination.
FAQs
Is diarrhea in dogs always serious?
Absolutely not. While one bout of loose stools in a healthy, happy, bright dog will likely pass away with no further issues, persistent, severe, bloody, or recurrent diarrhea warrants veterinary care.
How long can diarrhea last in a dog?
It really all depends on what is causing it. Mild food sensitivities, or some degree of stress-related bouts, usually subside fairly quickly. Infections, parasitic infestations, chronic enteropathy, and systemic disease can continue to plague your pup or return. Since it’s better to err on the side of caution, consult your vet as soon as possible if you see that your pup has frequent diarrhea that is getting worse, or is showing other symptoms.
Why does my puppy have diarrhea?
Your pup could be experiencing diarrhea due to the transition in diet, parasites such as giardiasis, bacterial/fungal infections, etc. Due to their small stature and ability to get dehydrated quickly when they vomit or have excessive diarrhea, it is best to seek veterinary care.
Why is there blood in my dog’s diarrhea?
Red fresh blood may appear where the colon is inflamed or irritated, and a variety of severe gastrointestinal illnesses may also result in bloody stools. The presence of blood does not necessarily determine the underlying cause of your dog’s condition. Bloody diarrhea that occurs frequently along with vomiting, lethargic behavior, weakness, and/or dehydration should receive prompt veterinary evaluation.
Can I give my dog antibiotics for diarrhea?
Absolutely not. According to WSAVA/ENOVAT guidelines, most mild to moderate instances of acute canine diarrhea do not warrant antibiotics at this time.
Final Takeaway
Why does my dog have diarrhea? There isn’t one correct answer to this question. Diarrhea in dogs can result from eating something unusual (like spoiled food), too many changes in their diet at once, being stressed out, having parasites or infections, or suffering from pancreatitis, an intestinal obstruction, or some type of chronic illness/medical issue.
It is also dependent on how bad it is, how long you’ve had to put up with it, what your dog’s stool looks like, what else has been happening along with the diarrhea, and your dog as a whole.
If your dog has a mild case of diarrhea that is otherwise perfectly fine, then there may be times that just providing the proper supportive care will help them recover. However, if your dog vomits often enough that they have lost significant amounts of blood, if they are severely depressed/dehydrated, if your dog is showing signs of extreme abdominal pain, if you suspect your dog ingested a toxin or object, or if your dog’s health rapidly deteriorates due to diarrhea, then I would recommend taking your dog to see a veterinarian.
Veterinary Review
Reviewed by Dr. Muhammad Usman, DVM, RVMP, Pakistan, Qatar-licensed Veterinarian
This article is intended for general pet-owner education and does not replace an individual veterinary examination, diagnosis, or treatment plan. The appropriate management of diarrhea depends on the dog’s age, health status, hydration, clinical signs, and suspected underlying cause.
References
- Merck Veterinary Manual. Introduction to Digestive Disorders of Dogs. Updated 2026. (Merck Veterinary Manual)
- Merck Veterinary Manual. Disorders of the Stomach and Intestines in Dogs. (Merck Veterinary Manual)
- Merck Veterinary Manual. Principles of Treatment of Gastrointestinal Disease in Animals. Reviewed July 2025. (Merck Veterinary Manual)
- Merck Veterinary Manual. Noninfectious Diseases of the Gastrointestinal Tract in Animals. Updated August 2025. (Merck Veterinary Manual)
- Companion Animal Parasite Council (CAPC). Giardia Guidelines for Dogs. Updated August 3, 2026. (Companion Animal Parasite Council)
- WSAVA/ENOVAT. Guidelines for Antimicrobial Use in Canine Acute Diarrhoea. (wsava.org)
- Merck Veterinary Manual. Acute Hemorrhagic Diarrhea Syndrome in Dogs. Updated June 2025. (Merck Veterinary Manual)
- VCA Animal Hospitals. Urgent Care for Diarrhea or Vomiting. (VCA)
