Possible Medical Causes of Aggression

Many conditions can cause unusual or aggressive behavior in dogs:  anything from teeth and eyesight to joint pain.

Many conditions can cause unusual or aggressive behavior in dogs:  anything from teeth and eyesight to joint pain.  If the temperament problem is genetic, then the likelihood that you can completely cure the aggression in the animal is minimal. The treatment would then concentrate on the “management” of the behavior rather than an absolute cure.

Medication prescribed by your veterinarian can effectively treat other conditions (like hypothyroidism). Any condition which causes inflammation of the brain can also cause neurological problems, including aggression. A chemical imbalance can make their behavior unstable, and they may require medication to rectify the situation.

You should rule out all possible medical causes BEFORE you consult a trainer at the onset of any sign of aggression.  Suppose an injury, disease, or congenital genetic disability is deemed the cause of the dog’s mood swings or aggression. In that case, no training will be effective until the problem has been resolved or controlled.

Medical conditions that have been linked to aggression in dogs 

Brain Chemistry

Cognitive Dysfunction Syndrome, associated with age-related degeneration, can be managed through medication and environmental and behavioral modification. This condition is not unlike clinical depression, obsessive-compulsive disorders, etc., in humans. Serotonin plays a vital role in the neurochemical control of aggression in the brain, especially when impulsivity is present. As with humans, the family of SSRI drugs has the most success combined with “therapy,” i.e., behavior modification techniques. There are not many behavior cases that will respond to medication alone.

Hypothyroidism or low T4 

A common endocrine disease where the body produces an abnormally low amount of thyroid hormones. Autoimmune destroys the thyroid gland, which affects more than 50 dog breeds and crosses.

Encephalitis (bacterial or viral)

Distemper and rabies are viral forms of encephalitis.  There are two common forms of encephalitis: acute encephalitis in young dogs or puppies and chronic encephalitis seen in older dogs, even those with a good vaccination history.


This is a medical term meaning low blood sugar. Symptoms of a hypoglycemic attack can include staggering or collapse, weakness, aggression, moodiness, glassy eyes, staring, dazed look.

Hydrocephalus in brachycephalics

Also referred to as “water on the brain.” t is a condition that affects the toy breeds and the brachycephalic dogs with very short noses, like the boxer, pug, etc.


There are many causes of epilepsy, so diagnosis is not always easy.  Primary epilepsy is a hereditary condition that is more common in certain breeds.  Other causes include canine distemper, encephalitis, meningitis, poisonings, liver and kidney disease, head injuries, brain tumors, strokes, cerebrovascular disease, hydrocephalus, etc.  Many of the causes of epilepsy remain obscure.

Brain tumors

A brain tumor can cause changes in temperament. An animal afflicted might observe some or all of these changes at varying times and degrees:  changes in mental status, aggression, confusion, irritability, increased vocalization, apathy, hyperexcitability, tremors, weakness, disorientation, visual deficits, circling, falling, irregular sleep habits, abnormal postures, exaggerated gait, head tilt, pain, house soiling, staring, trembling, decreased appetite, seizures, paralysis.

Head trauma

Swelling or bleeding may result when the brain has suffered trauma or injury. This swelling or bleeding will interfere with the normal function of that part of the brain. Many unusual neurological symptoms can result, including aggression.

Behavioral seizures

Also referred to as “age syndrome.”Partial seizures occurring in a brain region that controls aggression can cause sudden, unprovoked aggression.

Final Note

A dog in pain can react defensively or aggressively.  Always consult your veterinarian should your dog become aggressive.  They will rule out any medical problems.  A behavioral trainer can then teach self-control and boundaries to help you manage the dog.

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