Very often if your dog has an upset stomach, it starts at nighttime. Many pet parents have either been woken up by a dog barking or scratching to go out or alternatively come downstairs in the morning to find a mess that needs clearing up!

It’s not always the case that your dog will have started having diarrhea at night—many dogs can get an upset stomach in the day too, but perhaps it’s just that we notice it even more at night. Your dog is usually shut indoors at nighttime and unable to just go off to the toilet when he needs to. Couple this with the fact that your dog’s gut transit time (the time food takes to pass through the digestive tract) has probably been sped up by the underlying trigger, meaning your dog may get caught short!

In this article, we look at some common causes of diarrhea in dogs and what you can do to help.

Why does my dog have diarrhea at night?

1. Dietary changes


Recent changes in diet can cause digestive upset, especially if the change in food was made suddenly. When swapping your dog onto a different type or brand of food, it is best to make a gradual transition, mixing in the new food with some of the old food over several days.

Similarly, if your dog eats a lot of table scraps or tidbits these could cause diarrhea, especially if they are much richer than he is used to. Some dogs can also get tummy upsets by eating things they shouldn’t do, like discarded food or manure while out on a dog walk. This is called dietary indiscretion and some dogs will snaffle all sorts while out and about!

2. Food intolerance/allergies

Dogs can suffer from underlying food allergies or intolerances to certain ingredients. Allergens can be ingredients that dogs come across commonly in commercial food, like chicken, beef, and cereals such as soybean. Some dogs can react to more than one allergen too.

Food allergies are only officially diagnosed once other conditions have been ruled out by your veterinarian, and with the help of a proper food trial. This usually involves feeding your dog solely on a novel protein diet or a hydrolyzed diet for at least 6-8 weeks, before challenging it with ingredients that are introduced one at a time to see if they produce a reaction.

If you suspect your dog has an allergy or intolerance then speak to your veterinarian for more advice.

3. Antibiotics/medication

Certain medications can have the potential to cause side effects in some individuals. Antibiotics are well known for causing tummy troubles. They can affect the good gut flora in your dog’s digestive system, as well as battling the bad bacteria that they are being taken for. This can cause the unwanted side effect of diarrhea. Taking probiotics and replenishing the good bacteria can help counteract this.

Other medications like non-steroidal anti-inflammatories (NSAIDs) can cause diarrhea too. These medications are usually taken as pain relief or because of their anti-inflammatory properties, and for most animals, they are taken without issue. However, some dogs may develop unwanted side effects.

If your dog is on any sort of medication and develops diarrhea, speak to your veterinarian for advice.

4. Illness/disease

Diarrhea is a non-specific system and so can occur in many illnesses or disease processes.

Parasites like worms and the protozoa Giardia can cause loose stools, as well as bacteria like campylobacter or salmonella. Viral infections like parvovirus can cause serious diarrhea, especially in unvaccinated dogs. Foreign bodies are indigestible objects that have become trapped in the digestive tract and can cause diarrhea. Common examples include corn cobs, stones, fruit pits, socks, and toys.

Pancreatitis can cause diarrhea alongside other symptoms like vomiting and severe abdominal pain. The pancreas is a small organ involved in the digestion of fats and when this becomes inflamed it can have knock-on effects for the rest of the digestive tract.

Inflammatory bowel disease (IBD) is another condition that can cause an array of symptoms like diarrhea, vomiting, and weight loss. Diagnostic tests are needed to confirm this illness, which is usually controlled through a change in diet and medications.

Hormonal conditions like Addison’s disease can cause diarrhea, as can certain types of cancer.

5. Anxiety, stress, or emotional distress


For some animals, stress or anxiety can cause diarrhea. This could occur during sudden onset events like fireworks or thunderstorms, or through chronic stresses like being bullied by another pet or feeling anxious when being left on their own. There are often other symptoms that accompany diarrhea including restlessness, vocalizing, destructive behaviors, and changes in appetite.

Calming pheromone products can help some pets, in conjunction with behavioral training and ensuring they are getting plenty of exercise and positive mental stimulation. Taking advice from a qualified pet behaviorist can be helpful for some animals.

How to know if your dog has a serious stomach issue

If your dog has a serious stomach issue they will usually appear unwell or depressed. They may be off their food and have other symptoms like vomiting, lethargy, and weight loss. Profuse, watery, and/or bloody diarrhea are signs that there may be a serious disease process going on too.

How to know if your dog has anxiety, stress, or emotional distress

Dogs with behavioral issues will usually show other signs as well as loose stools. These dogs will appear on edge or stressed, which often manifests as being restless or unable to settle. Some dogs may become destructive, scratching or chewing at things. Vocalization like howling or barking may be noticed too, especially when you leave them on their own.

Nighttime diarrhea in puppies

Many puppies can have mild digestive upsets, especially when they first come to a new home. Changes in diet and the stress of leaving their mother and siblings can cause tummy troubles. Most young pups are not yet house trained, which makes accidents overnight more likely. They may not be used to being on their own overnight either, contributing to feelings of anxiety.

Make sure you aren’t feeding your puppy too late at night, otherwise he won’t have had a chance to empty his bowels before he goes to bed, making accidents more likely.

In most cases, soft stools will resolve without too much intervention. However, bear in mind that puppies can also be carriers of parasites or bacterial infections, which would require treatment.

Nighttime diarrhea in senior dogs

Senior dogs are more likely to develop diarrhea because of underlying health conditions or because of medications that they are taking. While the odd bout of mild tummy upset is probably nothing to be worried about, if it is happening frequently or you are seeing other symptoms then your old dog probably needs checking over by a veterinarian. Older dogs may also start to suffer from incontinence issues due to weakening muscles.

When to take your dog to the veterinarian


You should always take your dog to the vet if you are worried about them—it’s best to get things checked early on, rather than ignoring it. Symptoms that definitely warrant a trip to the vets would include profuse, watery diarrhea, bloody stools, abdominal pain, and vomiting. If your dog is becoming lethargic or off his food then this could be a sign of dehydration so again, get him checked out. Weight loss would be another cause for concern and may be seen in cases of chronic diarrhea.

Your veterinarian may need to run some tests to reach a diagnosis. This could include fecal sample analysis, blood tests, and diagnostic imaging like x-rays and ultrasound scans.

Mild cases of diarrhea may respond well to some bland, easy-to-digest food (like cooked chicken and boiled rice) and probiotics, so you could always choose to try this initially if your dog is otherwise well in himself.


There are many reasons why your dog might be passing diarrhea at nighttime. This article has looked at some of the common ones, but your veterinarian will be able to advise you further depending on the findings of any investigations they perform. Make sure you don’t feed your dog too late at night so that they have time to go to the toilet before bed and ensure they are up to speed with preventative treatments like worming and vaccinations. Above all seek help if you are worried about your dog in any way.