What are Some Common Medical Causes of Aggression in Dogs?

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  • Written By: Sheri Cyprus
  • Edited By: Bronwyn Harris
  • Last Modified Date: 06 October 2019
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Aggression in dogs can have a medical base. Medically-induced aggression can result in growling, snapping, showing teeth and positioning the body in a dominant stance. Medical causes of aggression in dogs include hypothyroidism, hypoglycemia and brain inflammation.

Brain inflammation that occurs in conditions such as encephalitis is one of the most serious medical causes of aggression in dogs. Rabies and distemper are both types of viral encephalitis. In cases of brain inflammation due to diseases such as encephalitis, the aggression is usually a neurological reaction to the affect of the inflammation on the brain.

Hypoglycemia, or low blood sugar, is another possible cause of aggression and may or may not be related to diabetes. Dogs with low blood sugar may feel disoriented and strange. If they feel vulnerable, they may behave aggressively in order to avoid appearing weak. Dogs with low blood sugar may appear glassy-eyed with a staring look. Weakness or collapse may occur. A veterinarian can perform a simple blood test to diagnose hypoglycemia.

Hypothyroidism is one of the most common medical causes of aggression in dogs. Very low thyroid levels affect mood. Thyroid replacement therapy has worked to relieve aggression in dogs with hypothyroidism in some cases. Weight gain, lethargy and the loss of a large amount of hair are other symptoms of hypothyroidism.


Over 50 different breeds and cross breeds are susceptible to hypothyroidism, and it is one of the most studied causes of dog aggression. Behavioral changes, especially aggression, are often the earliest signs of this condition. Even a dog that was once friendly to strangers may become aggressive if it has extremely low thyroid levels. A veterinarian can conduct a blood test to diagnose hypothyroidism.

Medical causes of aggression in dogs may sometimes be more subtle than growling and snapping. A dog may suddenly begin to stand on people's feet or block doorways as a way of exerting dominance. Cognitive Dysfunction Syndrome (CDS), sometimes called "dog's Alzheimer's disease," is thought to be another cause of aggression. CDS may lead to behavioral changes due to the loss of brain cells caused by brain degeneration.


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Post 3

@Latte31 -I agree with you. I think that dog behavior is related to how the animal is treated. The most aggressive dogs that I have ever seen are always chained up.

I think that this fosters aggressive dog behavior because it is an unnatural state for the dog to be in and he is fighting it with his aggression. If the same dog were loose inside of a house or even in the backyard the dog would not be so aggressive.

I think that dogs that are mistreated become conditioned to be aggressive because that is the only way that they can protect themselves which is really how you learn to understand aggressive behavior in dogs.

Post 2

@Panda2006 -I agree with you. I think that dog problems or aggressive dog behavior is often a result of how the dog is socialized. For example, some breeds have an aggressive and violent reputation but that is not true for every dog representing that breed.

For example, where I live, pit bull dogs are illegal to own because of documented cases of the animal becoming violent and killing or hurting other people.

However, my husband had a pit bull growing up and it was his favorite dog. The dog was very loving and protected my husband from another aggressive dog that was going to hurt my husband.

Since this dog grew up in a loving environment he

remained that way through her life so you really can’t ban a breed because some of these dogs were raised to be aggressive.

Aggressive behavior in dogs is really a sort of conditioning that occurs when they are puppies. The dog’s training determines his behavior because no dog is born being aggressive that is something that they are taught to be.

Post 1

Dogs that have been neglected are often aggressive, and while this relates to their loneliness and lack of training, it can also be a sign that the dog is malnourished or otherwise suffering nutritionally. Dog health can affect aggression in psychological ways as well, such as if an owner goes from being very kind to being violent; some dogs would quickly return the favor, being suddenly anxious all the time,much like a child might in that situation.

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