Sudden weight loss in dogs


  • Weight loss in dogs has many different causes.
  • If you think your dog might be losing weight it’s important to have them checked, and to tell you vet about any other symptoms you’ve noticed, such as vomiting, diarrhoea, low energy, or changes in their appetite and thirst.
  • It’s also important to weigh your dog regularly so you can tell if they have started to lose weight.
  • Contact your vet if your dog is losing weight.

General information

If your dog is losing weight unexpectedly, it could be a sign of illness. There are many different causes of weight loss - some of them minor and easy to solve, others more serious.

It’s a good idea to check your dog’s weight and body condition score from time to time, especially if you notice a change or if their appetite increases/reduces. Your dog’s weight will naturally change by small amounts over time (especially as they get older), but if you have noticing them constantly getting thinner, or losing weight very quickly,
this could be a cause for concern.

If you think your dog is losing weight it’s always a good idea to think if there have been any other changes that might be linked, for example have you changed their diet or the amount they’re eating.

We have a separate guide if you’re looking for advice to help your dog lose weight.


Weight loss in dogs is usually only a concern if it happens suddenly, or when there isn’t an obvious cause. If your dog is losing weight, it’s important to tell your vet about any other symptoms you have noticed, such as:


There are many different conditions that can cause weight loss in dogs, some of the most common include:


If your dog isn't getting enough calories they often will lose weight. If your dog is losing weight, but seems otherwise healthy, have a think about whether they are:

  • getting enough food/calories for their size
  • eating less than usual
  • growing quickly (so needing more calories)
  • having their food eaten by another pet
  • doing more exercise than usual (so needing more calories)
  • pregnant or feeding puppies (so needing more calories).

Gastrointestinal (tummy) problems

Gradual weight loss is a common symptom of many different gut problems, such as chronic diarrhoea, protein losing enteropathy, stomach ulcers and IBD.


Many types of cancer cause weight loss or muscle wasting, which can be gradual or very sudden.

Kidney disease

Kidney disease often causes weight loss as well as increased thirst, and other symptoms such as smelly breath, diarrhoea and vomiting.

Dental disease or mouth pain

Dental disease and mouth pain can stop your dog from wanting to eat and cause them to lose weight.

Liver disease

Liver disease often causes weight loss and other symptoms such as increased thirst, vomiting, diarrhoea and jaundice (yellow lips, skin and eyes).


Diabetes is a condition that stops your dog being able to control their blood sugar levels. It causes rapid weight loss, changes in appetite, increased thirst, and is likely to make your dog pee a lot more than usual.

Heart problems

Heart problems can lead to weight loss as well as symptoms such as coughing and low energy.

Addison's disease

Addison’s disease is a rare hormonal problem caused by a lack of steroids in the body. It causes symptoms such as weight loss, vomiting, weakness, drinking and peeing more and collapse.

Old age

Most dogs lose a certain amount of weight as they age, especially as their muscles start to shrink. However, if your dog is losing a noticeable amount of weight as they age, it could be caused by something more serious so always have them checked by your vet.

Exocrine Pancreatic Insufficiency

Exocrine Pancreatic Insufficiency (EPI) is an uncommon condition that causes very dramatic weight loss and diarrhoea. It’s most common certain breeds such as German Shepherd dogs.

When to contact your vet

Always contact your vet if you think your dog is losing weight, especially if they seem to have lost a lot in a short space of time.

If you’re unsure whether your dog is losing weight, you might want to weigh them every few days (for a couple of weeks) and take this record to your appointment. It’s also a good idea to keep a record of the food your dog is eating in the time leading up to the appointment, especially if you have recently changed their type or amount of food.

Consider taking out dog insurance as you bring your dog home, before any signs of illness start. This will give you peace of mind that you have some financial support if they ever become unwell.

You know your dog best. If they don’t have the exact symptoms listed above but you are still concerned it’s always best to contact your vet.

Published: September 2020

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.