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How to Tell If Your Dog Is Sick and When to Call the Vet

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Know when to call the vet by recognizing these signs.
Dog resting his head over the arm of a couch looking tired.

You come home and your dog isn't waiting by the door for you. They aren't wagging their tail looking to play fetch. The food in their doggy bowl is left untouched. Their posture has stiffened. You can tell something is wrong — and you're probably right. 

While dogs can't tell you they're sick, they can show you by exhibiting signs they aren't well. These range from behavior changes, lethargy and weight fluctuations to more obvious red flags such as vomiting and diarrhea. 

Remember that you know your dog best and if anything feels off, it's probably a good choice to call your vet to see if a visit is needed.

These seven signs can help you tell if your dog is sick.

1. Change in Behavior

Changes in your dog's behavior can be subtle, but keep a close eye on them if they alter their routine. If your dog always waits for you by the door and doesn't for two days in a row, something is likely bothering them. If your gentle, happy dog is suddenly snapping and growling, that's a clear sign something is wrong. Or is your pup panting more than usual? Sleep changes, constant pacing, increased aggression, whining, disorientation and refusing to leave your side are other clear behavioral changes that could indicate your dog is suffering. 

Sometimes these behavior changes are part of the aging process for dogs, but other times they can indicate problems, such as pain (an ear infection, for instance), arthritis or age-induced memory loss. Or it could be something worse. These behaviors can be symptoms of brain tumors or even dementia, known as cognitive dysfunction syndrome.1

Dementia in dogs is similar to Alzheimer's disease and typically affects older canines' memory, behavior and other cognitive functions. If your dog is suddenly having accidents or refusing to play fetch, they may have cognitive dysfunction syndrome. While this problem gets gradually worse over time because there's no cure, dogs with dementia can still live happy, active lives. Visiting a veterinarian early is key to developing a plan. Treatment involving routines, exercise and prescription drugs that increase dopamine activity in the brain have been proven to slow the progression of the disease. 

Behavior changes paired with other problems in appetite, lethargy and physical differences increase the risk that the problem is serious and your dog should be taken to a veterinarian. 

2. Lethargy

Some dogs prefer to lounge around, and many people have lazy pups. Dogs will sleep longer and longer as they age, too. However, a dog breaking their routine and becoming more lethargic than usual can be a sign of a larger problem. If your dog usually rushes to your side after you bring in the morning paper or sprints to their doggy bowl after you fill it with water, but has suddenly or gradually slowed down their pace, this is a sign your dog could be weak and suffering from an illness or injury. 

Lethargy is a symptom of infections, chronic pain or even life-threatening diseases. Several infections, such as parvovirus2, kennel cough3 and heartworm disease4, will make your dog appear very tired. Heart problems, liver problems and diabetes can also leave your dog weak and lethargic. 

Lethargy is a symptom of several serious health conditions. Early detection of these diseases and illness can lead to healthy recoveries. 

3. Weight Change

Weight fluctuation is a common sign of illness for dogs, but it may be hard to tell if your dog is getting heavier or lighter. People typically don't weigh their pets, so they may not even realize their dog has lost weight. You can easily weigh small dogs with your home scale, and you can usually stop by your veterinarian's office for free and do a quick weigh-in. Remember that, for smaller dogs, even losing one pound could mean a change in more than 10% of body mass. 

Weight loss is a symptom of cancer, intestinal parasites, gastrointestinal (GI) disorders5 and chronic renal failure6, among other disorders. GI disorders affect a dog's stomach and intestines and often affect digestion; they can be caused by allergies, eating a nonedible object or hereditary problems. Chronic renal failure (kidney disease) can be caused by infection or poison (make sure your pup never rummages through the medicine cabinet), or it can be inherited — in which case it can only be managed. Vomiting and diarrhea are also major symptoms of GI disorders and chronic renal failure. 

Weight gain can also be a major symptom of sickness. Your dog may love to eat, but if their belly starts dragging on the floor or looks bloated, this could be a sign of tumors, heart disease, hypothyroidism7 or Cushing's disease8, among other ailments. 

Hypothyroidism is common in certain dogs, such as golden retrievers and Doberman pinschers, and can be treated with hormone replacement therapy. Cushing's disease occurs when a dog produces too much cortisol and can be caused by tumors; a common symptom is a pot belly. A vet visit can help determine the cause for your dog's weight gain or loss.

4. Vomiting

Your dog vomiting isn't necessarily unusual and could be the result of eating too fast or too much. However, vomiting can also be a symptom of serious illness, including digestive problems, kidney disease, liver disease or a rupture in the esophagus. Check your dog's vomit for random objects, bone fragments and blood. If any of these appear, a trip to the veterinarian is in order. Also, remember that excessive vomiting can lead to dehydration. 

Kidney disease6 and liver disease9 can be the results of age, breed and/or poisonous substances ingested. These diseases will likely need to be treated for the rest of your dog's life. 

5. Diarrhea

Diarrhea isn't always a sign to panic, and can be brought on by something as simple as introducing a new food into your dog's diet. However, it can also indicate a major problem if it occurs frequently — especially if accompanied by vomiting and other symptoms such as lethargy and loss of appetite. 

Stool containing blood or mucus is a sign your dog needs medical care and should see a veterinarian. Watery diarrhea is also a major problem and excessive diarrhea can lead to dehydration. 

Parvovirus is one of the more serious diseases linked to bloody diarrhea2. This illness afflicts young puppies or unvaccinated dogs and leads to other infections. A dog that has diarrhea from parvovirus will likely need a hospital trip and prescription drugs. If treated, dogs have a 75% chance of survival from parvovirus; untreated parvovirus cases often lead to death. 

6. Change in Appetite

Sudden change in how much a dog eats or overeating are obvious signs that something isn't right. Just as humans don't want to eat when they aren't feeling 100%, neither do dogs. While dogs may eat less because of common factors such as rising temperatures outside or stress, a loss of appetite coupled with other symptoms can be a sign of liver disease, kidney disease, infection, cancer or even dental disease.10

If a dog has an infection or inflammation in their gums or mouth, it may be painful to eat. In addition to loss of appetite, owners can check their pups for bleeding in the gums, mouth irritation and excessive drooling. Dog owners should also develop a dental hygiene routine including teeth brushing to avoid periodontal disease and help keep their dogs happy and healthy. If you notice pale gums, take your pet to the vet right away. 

Loss of appetite can be a symptom of a lot of different ailments and should always be taken seriously. Increased appetite could be a sign of illness as well, including diabetes11 or hormonal problems. 

Dogs with diabetes are often ravenous because their bodies aren't allowing them to receive all the nutrients they need, despite keeping a steady diet. Diabetes is ultimately very treatable if caught early. 

Your dog may be nibbling on the outer edges of the dog bowl or licking their plate clean and asking for seconds. If this behavior isn't normal, it's important to consult a veterinarian to determine if sickness is the problem. 

7. Excessive Drinking and Urinating 

Increased thirst could be a sign of several diseases or illnesses, including urinary tract infections12, diabetes and kidney disease. If your dog is drinking a lot, they're probably urinating a lot, too. This can be another sign of possible sickness. 

Other problems with urinating, including frequent accidents and straining, can be symptoms of bladder or kidney stones, hormonal disorders and kidney and liver disease. 

More than 10% of dogs contract a urinary tract infection at some point in their lives, so keep an eye out for accidents, straining or frequent trips outside. Undetected UTIs can lead to cancer, painful stones and kidney disease. 

When to See Your Vet 

If you recognize your dog has exhibited more than one or several different symptoms, it's a sign your pet needs to see a veterinarian right away. And even if your dog doesn't exhibit any of these signs of illness, don't hesitate to take them to the vet if they're acting out of character, or if you have any concerns about their health. 

No one knows your dog as well as you. Trust yourself and your instincts. Always err on the side of caution and your pup will be back at your door, wagging their tail, ready for games and chowing down on their food in no time. 


  1. Cognitive Dysfunction Syndrome. (n.d.) Retrieved May 31, 2020, from
  2. Burke, A. (2021, May 26) What Every Puppy Owner Needs to Know about Parvo in Puppies. Retrieved October 25, 2021, from
  3. Kennel Cough in Dogs — Symptoms, Treatment and Prevention. (2019, January 23) Retrieved May 31, 2020, from
  4. Center for Veterinary Medicine. (n.d.) Keep the Worms Out of Your Pet’s Heart! The Facts about Heartworm Disease. Retrieved October 25, 2021, from
  5. Gastrointestinal and Digestive Disorders in Dogs: Types and Causes. (2015, September 11) Retrieved October 25, 2021, from
  6. Managing Kidney Failure in Dogs. (2018, November 6) Retrieved October 25, 2021, from
  7. Flowers, A. (2018, November 8) Hypothyroidism in Dogs: Symptoms and Treatment. Retrieved May 31, 2020, from
  8. PetMD. (2019, October 08) Cushing's Disease in Dogs. Retrieved May 31, 2020, from
  9. Facts about Liver Disease in Dogs. (2015, August 22) Retrieved October 25, 2021, from
  10. Fries, W. C. (2012, September 27) The Perils of Gum Disease in Dogs. Retrieved May 31, 2020, from
  11. Diabetes in Dogs: Symptoms, Causes and Treatment. (2019, November 05) Retrieved May 31, 2020, from
  12. Burke, A. (2019, November 06) Does Your Dog Have UTI Symptoms or Something Worse? Retrieved October 25, 2021, from


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