Medical Causes of Aggressive Behaviors in Dogs

Updated on March 13, 2018
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Adrienne is a former veterinary hospital assistant, certified dog trainer, behavior consultant, and author of "Brain Training for Dogs."

Hypothyroidism is seen often in Rottweilers..

medical causes of aggression in dogs,
medical causes of aggression in dogs,

It is an unfortunate fact that often dog owners feel compelled to give up on their canine friend as soon as he displays aggressive behaviors by either giving him away, or worse, surrendering him to a shelter or permanently solving the problem by putting him down.

Yet, there are cases where aggressive behaviors in dogs can be traced down to unforeseen medical conditions. What owners therefore may perceive as out of the blue, unprovoked aggressive attacks, can be instead attributed to something as justifiable as it can be from a dog's perspective: pain.

Veterinarians know this very well. In every veterinarian office tucked away in a handy drawer lies a set of different sized muzzles ready to be used. They know as a fact that even the most docile dogs may easily turn into vicious and snarling monsters at the sight of a needle or upon being treated for a painful wound.

Yet, while in these cases, the pain is visible to the eye and quite obvious, there are sometimes medical conditions in aggressive dogs causing very subtle, insidious symptoms that can be hardly recognized and detected by even the most attentive owners.

Owners of normally well mannered and well tempered dogs should suspect a medical condition when their dog acts aggressively out of the blue or in a gradual, yet, steady manner. Medical conditions should be suspected as well in stray dogs or rescue dogs with an unknown medical history. However, not all owners are willing to give these dogs the benefit of doubt, either out of ignorance (not knowing that there are actually conditions causing aggressive behaviors) or out of fear (the dog is a scary, must get rid of him as soon as possible!).

Truth is, an aggressive dog is indeed a scary dog, especially when the aggression is targeted towards other pets, children and people. Such dogs are perceived as a liability, an animal too dangerous to be handled and is easily converted from man's best to man's worst enemy. A once much loved dog has progressively transitioned into a snarling animal ready to bite. While many cases of dog aggression are behavioral in nature, it would be unjust to simply assume so without first attempting to rule out something medically going on.

This is why it is imperative to have a dog seen by a veterinarian right before calling a behaviorist or sending the dog to a trainer. Indeed, reputable dog behaviorists should ask for proof of a medical exam before seeing the dog. A dog behaviorist will never be able to successfully fix a dog acting aggressively because of an underlying medical problem!

Medical Causes of Dog Aggression

Following are some medical conditions known to cause aggressive behaviors in dogs.

Chronic Pain

An underlying ear infection may cause a dog to growl or bite upon being touched near the head. Spinal and neck problems may cause aggression when the dog's collar is touched to put on a leash. Chronic disorders such as arthritis and hip dysplasia may cause grumpy behaviors. A recent study revealed that sudden outbreaks of aggression are often pain related.


This condition affecting the endocrine system of dogs is caused by a low count of thyroid hormones. This condition can be easily detected through a simple blood test. Affected dogs typically develop increased weight gain, hair loss, lethargy, low tolerance of cold, and behavior changes such as anxiety, fear and aggression. It is quite unusual for dog to develop aggression as a stand alone symptom when having this condition, however running a thyroid test is still worthy.The condition is easily treated with the long term administration of thyroid pills which will dramatically improve the dog's condition.


Dogs may develop aggressive behaviors in the post-ictal phase, following a seizure. Partial seizures in dogs that affect a particular portion of the brain responsible for regulating aggression may be also a contributing factor for aggression and aberrant behaviors. These types of seizures are often found in certain dog breeds such as a Cocker Spaniels, Springer Spaniels and Chesapeake Bay Retrievers.

Brain Conditions

Trauma affecting certain regions of the brain may cause neurological symptoms including aggressive behaviors. These may take place after the dog has sustained brain damage. Brain cancer found often in senior dogs may be another cause for such behavior changes. Encephalitis, the inflammation of the brain may cause significant aggression in affected dogs. Rabies and Distemper are forms of encephalitis. Hydrocephalus, a congenital condition where the brain's ventricles become enlarged may cause a variety of neurological symptoms, sometimes including aggression.

Low Calcium Levels in Nursing Dogs

Some dog owners notice their mellow female dogs starts acting aggressively towards their puppies. At times this aggression may stem from low calcium levels and therefore is worthy of investigation by a vet. Eclampsia is the medical term for low calcium levels which is often seen in dogs having trouble supporting the calcium demand associated with producing milk. It is often seen in the first 3 weeks of nursing.

On top of no interest or aggression towards the pups, affected dogs may develop restlessness, a stiff, painful gait, muscle spasms, trouble walking and seizures.

There are many more examples of medical conditions causing aggression in dogs. A dog reacting aggressively upon being pet on the head may be suffering from an undiagnosed ear infection, a dog suffering from arthritis may react defensively when laying down and feeling like he cannot remove himself from an irritating situation such as when being pestered by a child.

A hearing-impaired dog may easily startle and bite out of fear when approached without notice. A dog may turn grumpy when dealing with tooth pain. These are just examples of dogs that are dealing with pain and medical conditions that often cannot be detected by the most well meaning owners.

The first step therefore for owners of aggressive dogs is to keep the dog muzzled and sent up the vet's examination table. Owners really owe this to man's best friends especially during these times when dogs need help the most.

Questions & Answers


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      • jtrader profile image

        jtrader 19 months ago

        Good to remember people can act out because of these conditions too.

      • Darlene Sabella profile image

        Darlene Sabella 8 years ago from Hello, my name is Toast and Jam, I live in the forest with my dog named Sam ...

        Wow, what a fantastic hub, I learned so much and really enjoyed reading this. I have owned dogs all my life and have never owned an aggressive pet. Thumbs up my friend great job

      • theherbivorehippi profile image

        theherbivorehippi 8 years ago from Holly, MI

        Great information here! Yes, it is scary of an animal turns aggressive but the majority of time, they have a reason...being in pain or sick or sometimes even a toothache can really interfere with the attitude of animal. It's important that pet owners stop giving up on their animals, take responsibility and get to the root of the problem and find out what is actually wrong with them! Great hub!