Why Is My Dog Losing Weight?

If your dog is losing weight, you need to take action now. Causes can range from worms, to a bowl he doesn’t like, to cancer, or heart failure.


You should be concerned if your dog starts dropping weight without any effort by you. No increase in exercise and no change in diet. Before you jump to cancer concerns, let’s look at simple solutions for why your dog is losing weight first:

Parasites. Take a fresh fecal sample to your veterinarian. While internal parasites are more likely to cause weight loss in puppies, even adult dogs can be dragged down by a heavy parasite load. If your dog is losing weight, it makes the most sense to get that fecal sample, so you know what you’re dealing with and can deworm for that parasite. Whipworms can be the worst and might require multiple samples to be identified. Your veterinarian may decide to deworm your dog just in case, which is not a bad plan.

Dental disease. If your dog’s teeth, gums, or mouth hurt, he may not be eating normally. That, obviously, will contribute to weight loss. A dog who approaches his food but won’t eat may have a painful tooth or could be nauseous.

Environmental changes. Next, look at behavior and environment. Ask yourself these questions:

  • Is your dog eating his meals?
  • Is your other dog bullying him out of all or part of his food?
  • If he is not eating, has anything changed about where or when he is fed?
  • Have you changed foods or even flavors within the same brand?
  • Have you changed bowls or noticed a chip in his old one? For whatever reason, your dog may be unhappy with his bowl.
  • Is your dog in heat or is another dog in the house in heat? Hormonal turmoil can upset an entire household. Both males and females may decide to skip meals.

Serious Causes of Dog Weight Loss

If your dog appears to be eating his normal meals, he may later vomit the food back up once he is outside in your yard – and possibly (yuck, I know) another dog is cleaning it up or he’s vomiting in a spot you don’t normally notice. Watch him when he goes out to see and look at the vomit. Check his stool, too. He could be pooping blood. A soft stool or diarrhea could indicate an illness. Getting to the cause for weight loss in your dog due to vomiting and/or diarrhea requires a gastrointestinal workup by your veterinarian. This will likely include a blood chemistry panel, ultrasound, and/or radiographs.

Dogs with diabetes often eat voraciously but lose weight. The same is true of some dogs with cancer, although other dogs will stop eating well and become very finicky.

Dogs with serious heart problems may stop eating due to cardiac cachexia, which is unintentional weight loss due to heart failure.

Many metabolic disorders such as adrenal problems, hyperthyroidism, pancreatitis, and intestinal, liver, and kidney conditions can all cause unwanted weight loss.

Act Quickly to Help Your Dog

If you can’t quickly resolve the problem through the environmental reasons above for your dog’s weight loss, you need veterinary help. Unintentional weight loss in a dog is a call for heads up. Waiting will only make things worse.

With any luck, a fecal sample check or quick behavior and environment check will show a reason for the weight loss. Otherwise, the best course of action is a full veterinary exam and diagnostic workup.


  1. You beat me in posting EPI. I adopted Ginger, a 11-year-old mixed terrier 4-1/2 years ago with a lot of health issues and allergies. The next day I took Ginger to my vet andshe needed a dental to remove 7 abscessed teeth and even though she was eating well on a soft food diet she was still losing weight. I started researching her symptoms and asked my vet to test her for flukes which turned out she had them and was treated. She seemed to be feeling better but still not gaining weight. To make a long story short it turned out she has EPI. Ginger eats a home cooked diet and pancreatin enzyme supplements and is doing great and you would never know she is 16 years old.