Adrienne is a certified dog trainer and former veterinarian assistant who
partners with some of the best veterinarians worldwide.

Brain chemistry can cause fear and aggression.

Brain chemistry can cause fear and aggression.

Photo by Daniel Lincoln, via Unsplash

The Role of Chemical Imbalances in Dog Behavioral Problems

If you own an aggressive or fearful dog, you may be wondering what may trigger
those bouts of aggressive or anxious displays you witness and how medications
may play a role in the recovery process. Just as in humans, chemical
imbalances may occur in your dog’s brain and can play a primary role in the
behavior of your dog. Taking a look at your dog’s brain chemistry may be
helpful in many cases. Let’s take a virtual walk into your dog’s brain so to
have a generalized sense of what may be possibly going on in there.

In This Article

  1. What’s in Your Dog’s Brain and How Does It Affect His Behavior?
  2. What Medications Are Used in Dogs With Behavioral Problems?
  3. Do Medications Help Dogs?
  4. My Experience With Medications vs. Behavior Modification

What’s in Your Dog’s Brain and How Does It Affect His Behavior?

The brain of a dog is ultimately quite similar to the brain of humans in many

  • They both include a limbic system, where emotions and memories are stored.
  • Also, both brains share the same basic neural chemistry, explains Stanley Coren.
  • This means that just as humans, dogs may suffer from emotional problems such as anxiety, fear and anger.
  • This paves the path to behavioral problems such as depression, stress-related disorders, irrational fears and compulsive, obsessive disorders.

Neurotransmitters, which are an important component of brain chemistry in
humans and dogs, are chemical messengers responsible for carrying, boosting
and modulating signals between neurons. There are two types of

  1. Excitatory neurotransmitters : These excite the neuron, stimulating it to action. Examples are norepinephrine, epinephrine—aka adrenaline—and cortisol which are fight and flight hormones produced by the adrenal gland.
  2. Inhibitory neurotransmitters : These inhibit the neuron, decreasing its action. Examples include serotonin and GABA.
  3. Excitatory and inhibitory neurotransmitters : These can have both effects depending on the receptors. Examples are acetylcholine and dopamine.

Excitatory Neurotransmitters

Let’s take a closer look into these neurotransmitters and their role in canine


Also known as adrenaline, epinephrine along with norepinephrine and cortisol
participate in the flight and fight response by making your dog’s heart pump
harder, opening the airways, and increasing blood flow to major muscle groups
in response to a threat.


Along with epinephrine and cortisol, norepinephrine is a stimulant and
participates in the fight-or-flight response, by increasing your dog’s heart
rate. At the same time, norepinephrine is also a mood enhancer which explains
why along with serotonin, norepinephrine has a positive effect on the brain.


This steroid hormone is also released in response to stress along with
norepinephrine, epinephrine. When a dog gets into “flight or fight” mode, this
chemical is often released and is why it is often referred to as the “stress
hormone.” Karen Overall of the Center for Neurobiology and Behavior at the
University of Pennsylvania found that aggressive dogs displayed an increased
level of cortisol in their blood and in a similar fashion did dogs who were
fearful and anxious. A study determined that aggressive dogs had 21 units
compared to 10 in non-aggressive dogs.

Inhibitory Neurotransmitters


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This is a neurotransmitter found in the intestinal tract and central nervous
system. lt is thought to be responsible for general feelings of happiness and
well-being which is why it is often referred to as the “feel-good” hormone. A
study by researchers at Zaragoza University in Spain determined that dogs that
were aggressive had lower levels of serotonin in their blood. To be exact,
such dogs had 278 units compared to 387 in non-aggressive dogs.

Serotonin, unfortunately, cannot be supplied in the form of a pill or
injection. Interestingly though, a class of drugs known as tricyclic
antidepressants (TCA) helps slow down the reabsorption rate of the
neurotransmitters serotonin and norepinephrine, allowing their levels to rise.
A drug belonging to this class is clomipramine.

On the other hand, another class of drugs known as “selective serotonin
reuptake inhibitor,” often abbreviated as SSRI, helps block the reabsorption
of serotonin allowing more serotonin to be available for extended periods of
time, explains Certified Applied Animal Behaviorist, Benjamin L. Hart. Drugs
belonging to this class include fluoxetine, sertraline and paroxetine.

Note: Buspirone is a serotonin 5-HT Agonist known for activating serotonin
receptors, and mimicking the effect of serotonin.


GABA stands for Gamma-aminobutyric acid which is a neurotransmitter
responsible for regulating neural excitability. Benzodiazepines help enhance
the effect of this neurotransmitter, reducing the firing rate of neurons in
the central nervous system.

Excitatory and Inhibitory Neurotransmitters


“Dopamine helps coordinate the dog’s motor skills, attention, reinforcement
and reaction time and it has an impact on the brain’s mood area where “good
feelings” originate” explains dog trainer Nicki Tudge. When neurotransmitters
transfer excessive dopamine dogs can become agitated, impulsive and easily
reactive, creating an excitatory response. On the other paw, when dopamine
levels are reduced the dog becomes under-reactive, creating an inhibitory


This neurotransmitter at a cardiac level has an inhibitory effect, which
lowers heart rate. However, acetylcholine, may also behave as an excitatory
neurotransmitter at the neuromuscular level in skeletal muscles.

What Medications Are Used in Dogs With Behavioral Problems?

The most common class of drugs used in behavior modification are
benzodiazepines (BZs), monoamine oxidase inhibitors (MAOIs), tricyclic
antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs),
according to the ASPCA. These medications may be prescribed by a veterinarian
or board-certified veterinary behaviorist.

  • Acetylpromazine (Acepromazine)
  • Alprazolam (Xanax) BZ
  • Amitriptyline (Elavil) TCA
  • Buspirone (Buspar) serotonin 5-HT Agonist
  • Fluoxetine (Reconcile, Prozac) SSRI
  • Clomipramine (Clomicalm) TCA
  • Diazepam (Valium) BZ
  • Paroxetine (Paxil) SSRI
  • Propranolol (Inderal)
  • Selegiline (Deprenyl, Anipryl) MAOI’s
  • Sertaline (Zoloft) SSRI

Do Medications Help Dogs?

While behavior modification alone may help dogs in need and change emotions
and brain chemistry, it is also true that in certain severe cases, medications
may be needed so to stop the brain from interfering with learning appropriate
behavior. Following are some benefits and reasons why medications may be
needed in severe cases:

  1. When your dog is in a fight or flight state of mind, he is ready to react and not capable of learning. With medication, your dog will be calmer and has better chances for learning.
  2. Medications may speed up the learning process.
  3. Some medications such as benzodiazepine act quickly if given before exposure.

However, there are also cases where the use of medications, is counter-
productive and there are also disadvantages. Here are some of the cons:

  1. There are risks for side effects and paradoxical effects.
  2. As the dog is weaned off the medication there may be relapses.
  3. Most medications are not a quick fix, may need to be taken for a while before effects are seen
  4. Medications should not be used alone; but rather, along with a behavior modification program.

My Experience With Medications vs. Behavior Modification

While I am not a big fan of meds, I think in severe cases and in certain dogs
they do help take the edge off (by fixing imbalances in neurotransmitters) so
to open up the lines for learning so the dog can cognitively function. And
this is a good reason why vets should refer clients to trainers/behavior
consultants so the vet can take care of chemical imbalances and the
trainer/behavior consultant can handle the behavior modification process. This
partnership should help prevent veterinarians from unnecessarily increasing
dosages and owners from becoming frustrated because the “meds are not
working.” And in some cases, the dog may even not need any meds at all,
because the trainer/behavior consultant may have alternative
approaches/calming aids/methods up their sleeves.

I worked on a case with a behaviorist where the dog had inter-dog aggression
and the drugs were needed because according to the behaviorist the dog was
reactive no matter the distance. I had my doubts on this though. The fact is,
this dog was in a fenced area with the other dog at a distance in a separate
fenced area. It seemed to me the drugs were perhaps needed to make him
comfortable and work sub-threshold in “THAT setting.” If I had this case on my
own, I would have been curious to know if in a different setting and with more
distance it was possible to find a threshold “oasis” without the need for

A while back, I was called to work on a case of severe inter-dog aggression
where the dog was not walked for over a year in a neighborhood surrounded by
fenced dogs. There was little opportunity to find a comfortable threshold
distance here because of how the neighborhood was displayed. It took weeks of
daily work to get to the point of walking him past the dogs without reacting,
but we finally made it. So in my experience, drugs can make the process easier
and perhaps even shorten it, but I am not a big fan of them when vets
prescribe them because of obvious risks for side effects and the fact that
once the dog is weaned off, I have seen relapses (just as in people), whereas
with no drugs, the process took longer but the results seemed to be more
reliable, at least in my humble opinion.

What do studies say? “Drug therapy is rarely curative by itself and in most
cases is only indicated as ancillary therapy in a behavior modification
program” according to this abstract.

This article is accurate and true to the best of the author’s knowledge. It
is not meant to substitute for diagnosis, prognosis, treatment, prescription,
or formal and individualized advice from a veterinary medical professional.
Animals exhibiting signs and symptoms of distress should be seen by a
veterinarian immediately.


Lin Bauer from CapeTown South Africa on February 06, 2020:

Thank you I will try this next time, having him on a leash until he is calm.

Adrienne Farricelli (author) on February 06, 2020:

Hi Lin,

With anxious dogs like that, treatment generally falls more under behavior
modification rather than training. I would prevent him from having direct
access to guests to prevent rehearsal of the trouble behavior (nipping, acting
anxious) and would suggest keeping him distant with a leash (to keep him under
threshold) and gradually work on changing his emotions towards people coming
into the house. Because of the importance of correct implementation of
behavior modification and safety, it’s important to enlist the help of a dog
behavior professional using force-free behavior modification. Severe cases of
anxiety may require meds prescribed by the vet. This is just an example of the
type of work I did with a dog anxious about a person entering the home.…

Lin Bauer from CapeTown South Africa on February 05, 2020:

I have a very anxious 2 yrs old GSD he gets very anxious when people come to
my house, he is then unable to control himself and starts to nip,after a nip
he increases his distance & is very submissive. He is otherwise very obedient
we do go to training in a group every week where he is the “perfect” dog, he
gets anxious when there is a lot of excitement or sudden movement. He was
rescued at 6wks, his mother passed away at this time from abuse & neglect, I
got him at 3mnths. We immediately started puppy training. He is very
protective of my two granddaughters. I have a 15yr cocker spaniel who he
adores but every now and then he seem to “snap” and snaps at her grabbing her
by the ears, he has never hurt her or broken skin, immediately afterwards he
goes into a submissive position & goes to lick her face. I also have a 4yrs
Belgium Mallinois, & 1yr Swiss Shepherd, he has not behaved like that towards
them, he does get over excited when he plays with the Swiss & hurts her she
she then yelps & walks a way, or when I notice the play is escalating I will
say “gently” he then backs off & continues play more calmly. He is a high
energy dog, we walk for 1hr 5/wk, 2hrs beach walk x1/wk & obedience class with
play afterwards x1/wk. He was neutered at 9 Mnths, he does not do resources in
his food but does guard my granddaughter when he is in the room with her, my
daughter the other day opened the bedroom door & walked in without identifying
herself, he snapped & barked and nipped her on the leg.How can I do to help my
dog who is gentle except when these episodes happen.

Alexandra Bassett on May 26, 2019:

Great article. Very thorough overview. Thank you!

Adrienne Farricelli (author) on August 23, 2018:

John, before thinking about chemical imbalance, it may be worthy considering
other dyanamics taking place such as fear aggression or resource guarding.
Please consult with a professional to help determine the underlying dynamics
and triggers.

John Pryce on August 20, 2018:

I have a Jack Russell dog that sume time’s tries to bite dogs or people can
she have chemical imbalance

annerivendell from Dublin, Ireland on September 17, 2012:

Another great hub. What an interesting area too! Voted up.

Adrienne Farricelli (author) on September 16, 2012:

Nat Amaral, I agree dogs should get an individualized treatment plan since
they all respond differently to treatment. The one size fits all definitely
does not apply here.

Adrienne Farricelli (author) on September 16, 2012:

Thanks Mary, I am studying to further continue my education (this time
specializing in getting a canine psychology degree), so you will see more and
more articles tackling dog behavior for some time!

Nat Amaral from BC Canada on September 16, 2012:

I love this hub. Yes, I think there should be treatment for the aggressive dog
behavior because of some past experiences (bitten by 2 different dogs on 2
different occasions), but that should be done with some caution. Every dog
will respond to it differently, and in some cases, it won’t always be good.

Mary Hyatt from Florida on September 16, 2012:

As always, you have written a very informative Hub. You are certainly an
expert in canines and their behaviors. I’ve never had an aggressive dog, thank

My Miniature Schnauzer is an easy going dog for the most part.

I voted this Hub UP, etc. and I will share this good info.

Adrienne Farricelli (author) on September 16, 2012:

Thank you. Studies have shown that diet can have a calming effect on dogs. One
study suggests that tryptophan helps dogs suffering from aggression and
hyperactivity. This makes sense, since trytophan is know for causing
sleepiness in humans after drinking milk or eating chicken/turkey along with a
carbohydrate snack.

Larry Fields from Northern California on September 16, 2012:

Hi Alexadry. Loved your hub.

I used to take my neighbor’s family’s Border Collie mix on day hikes. I found
that a home-made ‘treat’, consisting mainly of Carob powder and butter-
flavored Crisco, had a slight calming effect on Gurr. When we stopped to eat
lunch, he would get that for ‘dessert’, after a handful of his regular kibble.
Milk Bone dog biscuits had the opposite effect. Go figure.

Voted up and interesting.