The short answer
Many vets suggest that diarrhea lasting longer than a day or two, or any diarrhea with other worrying signs, should be checked. Puppies, seniors, small dogs, and dogs with health conditions should be seen sooner. These are general guidelines, not a rule for every dog, so if you are unsure, a phone call to your vet or an emergency clinic is always reasonable.
Go to an emergency vet now if you see any of these
Seek urgent care if diarrhea comes with:
- Blood in the stool, either red streaks or black, tarry stool
- Repeated vomiting, or being unable to keep water down
- Severe lethargy, weakness, or collapse
- Signs of dehydration, such as dry or tacky gums or sunken eyes
- A swollen, hard, or painful belly, whining, or a hunched posture
- Constant straining with little or nothing coming out
- Possible swallowing of a toxin, medication, toy, or other object
- Pale gums, trouble breathing, or a very high or low body temperature
Call your regular vet the same day or next day if
- Diarrhea continues beyond a day or two, even if your dog seems fairly well
- Your dog’s appetite is down or they seem quieter than usual
- Diarrhea keeps coming back
- There is mucus in the stool, or the stool is very large or has a strong, unusual smell
- Your dog has recently started a new medication
- Your dog has lost weight, or has had several loose stools over weeks
Puppies, seniors, small dogs, and dogs with health conditions
These dogs can dehydrate and decline faster, and puppies may also not yet be fully vaccinated against infections that cause diarrhea (see the new puppy vet checklist for the usual vaccine schedule). For these dogs, many vets would rather hear from you early than late. Do not try a food fast or home remedies in a puppy or a dog with a condition such as diabetes or kidney disease unless your vet advises it.
How long is too long to wait?
There is no single safe number of hours for every dog. For a healthy adult dog who is bright, eating, and drinking, many vets are comfortable with a short period of watching. For anyone else, or when other signs appear, waiting is riskier. Diarrhea that is steadily getting worse should be seen promptly. If your dog has other symptoms in addition, treat the combination as more serious than either alone.
What causes diarrhea in dogs?
The most common triggers include eating something unusual, sudden diet changes, and stress. Other causes include intestinal parasites, viral or bacterial infections, food intolerance or allergy, medications, toxins, inflammatory bowel disease, pancreatitis, and obstruction. Because the list is so long, a vet may need a stool sample, an exam, or tests to find out why.
What to tell the vet
Having these details ready speeds things up:
- When the diarrhea started and how often your dog is going
- The stool’s appearance: watery, mucus, blood, color
- Any vomiting, appetite change, or low energy
- Anything new your dog ate, or may have eaten
- Recent diet changes, medications, or boarding or daycare visits
- Vaccination and deworming history
- Photos of the stool, and a fresh sample if asked
What the vet may do
Depending on your dog, the vet may examine your dog, check hydration, and ask for a stool test. Bloodwork or imaging may be recommended if your dog seems unwell. Treatment can include fluids, a diet change, medication aimed at the cause, or hospital care for dogs who are dehydrated or vomiting.
What you can do while you arrange care
Keep water available and keep your dog calm. Do not give human medicines or leftover prescription drugs. Do not force food. If your dog is only mildly affected and your vet agrees to home care, our guide to home treatment for dog diarrhea explains gentle supportive steps. If vomiting is also happening, see dog vomiting yellow: causes and treatment and the warning signs in dog intestinal blockage treatment.
Frequently asked questions
What is the “silent killer” of dogs?
There is no single answer, since several serious conditions can develop with few early signs. In the context of diarrhea, dehydration and an unnoticed obstruction or infection are good reasons not to wait too long with a dog who is getting worse.
What can I give my dog to stop diarrhea?
Ask your vet first. Fresh water and, for suitable dogs, bland meals may be recommended. Human anti-diarrhea and pain medicines can be harmful to dogs.
What is the most common cause of diarrhea in dogs?
Dietary indiscretion, meaning eating something unsuitable, is widely cited as a frequent cause, but it is not the only one. A vet can help if the cause is unclear.