PERCY'S PANORAMA — SPECIAL INVESTIGATIVE EDITION --- The CBD Question

The CBD Question: What the Science Says, What It Doesn't, What Nobody Has Noticed, and What Everybody Getting This Wrong Should Know

Percy here.

You are about to read the most forensically researched piece of dog content you have encountered this year.

I say this not to impress you — though I understand if you are impressed — but because I want you to know that what follows is the product of serious intellectual labour, and it deserves to be read with the appropriate level of attention.

Its deep, but so am I.

This is Percy's Panorama. My deep investigative format, reserved for subjects that require more than a news desk summary.

The subject today is cannabidiol — CBD — and its relationship with aggression in dogs.

You have probably seen the headlines. CBD calms aggressive dogs. 47,000-dog study shows CBD reduces aggression. The story has been circulating, and owners across the UK are asking questions about it. Some are already acting on it, without necessarily knowing that doing so may be technically unlawful. More on that shortly.

First, I want to take you through what the research actually shows. Not what the headlines say it shows. What it actually shows. Because the gap between those two things is, in my considered view, very significant indeed.

I am Percy. I am TSO. This is what I found.

PART ONE: THE DATA AND WHY IT MATTERS

In November 2025, a study was published in Frontiers in Veterinary Science drawing on data from 47,355 dogs enrolled in the Dog Aging Project — a long-term community science initiative in the United States in which owners complete annual surveys about their dogs' health and behaviour. It is the largest analysis of CBD use in companion dogs conducted to date.

The headline finding: dogs given CBD supplements over multiple years showed progressively lower aggression levels compared to dogs not receiving them. Anxiety and agitation did not show the same pattern. Only aggression.

This finding did not appear from nowhere.

A 2021 Italian placebo-controlled study of 24 shelter dogs found that 45 days of CBD significantly reduced aggressive behaviour toward humans. A 2023 Waltham study found a single dose of CBD reduced stress indicators during separation and car travel. The aggression signal, specifically, has now appeared across multiple studies with different designs, different populations, and different timeframes.

Something is consistently happening.

The researchers' conclusion was that CBD likely works by calming fear — because, they argued, most canine aggression stems from fear and anxiety. CBD reduces the fear response. The aggression follows.

Plausible. Logical. And, I will argue, substantially incomplete.

Because aggression in dogs is not one thing. It is at least seven things. Each with a different cause, a different neurological pathway, and a different relationship with any given treatment.

The researchers collapsed all of those into one category and offered one explanation.

That is where my investigation begins.

PART TWO: THE SEVEN FACES OF AGGRESSION

A proper map, since apparently one was needed.

1. Fear-Based Aggression

The most common form. The dog perceives a threat — real or anticipated — and aggresses to create distance or safety. Underpinned by the amygdala, the brain's threat detection system. CBD's proposed anxiolytic effects operate through serotonin 5-HT1A receptors and possibly via CB1 receptor activity in the amygdala circuit.

The researchers' explanation is reasonable for this type. Fear-based dogs may experience some relief. But this is one category of many.

2. Frustration-Based Aggression

A completely different neurological pathway, and the one the researchers appear not to have considered.

Frustration aggression does not begin in the amygdala. It begins when a goal is blocked — a resource, a destination, another animal — and the resulting arousal has no outlet.

The prefrontal cortex, the brain's executive control centre, is responsible for applying top-down inhibitory control over the deeper aggression circuits of the hypothalamus and periaqueductal grey. When that control breaks down — through high arousal, poor impulse regulation, or repeated frustration — aggression can emerge without fear being involved at all.

This matters for the CBD question because the endocannabinoid system is densely expressed in the prefrontal cortex. CBD is a documented agonist at serotonin 5-HT1A receptors, and cannabinoids have been shown to activate serotonergic neurons through the medial prefrontal cortex — the precise region responsible for inhibitory control.

Human neuroscience has established clearly that low prefrontal serotonin is specifically associated with impulsive aggression rather than fear-based aggression.

A 2022 pilot study from the University of Iowa compared chronic CBD users, THC users, and non-users on the Flanker Inhibitory Control and Attention Test — a standardised measure of the brain's ability to suppress impulsive responses. CBD users performed significantly better than THC users and similarly to non-users. CBD did not impair inhibitory control.

If anything, the signal pointed the other way.

These are human studies. I want to be explicit about that. The canine studies to test this hypothesis do not yet exist. But the neurobiological architecture is shared. Dogs and humans process impulse regulation through similar prefrontal circuits. The question of whether CBD modulates frustration tolerance and impulse control in dogs has simply never been asked.

It should be.

3. Pain-Induced Aggression

Arguably the most clinically important category, and the one that most directly challenges the conclusions of the 2025 study.

Pain causes aggression.

This is established beyond any reasonable doubt in the veterinary literature and dad talks about it all the time.

A 2025 review published in Frontiers in Veterinary Science found that between 30 and 80 percent of dogs referred for behavioural complaints had at least one underlying painful condition.

A clinical study from the Autonomous University of Barcelona examined 12 dogs with pain-related aggression and found musculoskeletal pain — predominantly hip dysplasia and elbow osteoarthritis — was the primary cause in 75 percent of cases.

The mechanism is direct. Chronic pain reduces serotonin activity in the brain, which in turn lowers the threshold for aggressive response. Pain also chronically activates the hypothalamic-pituitary-adrenal axis, maintaining a state of physiological arousal that amplifies every subsequent stress response. Dogs in chronic pain have, in the language of neuroscience, an overactive accelerator and an underperforming brake.

They arrive at the threshold faster and recover more slowly.

Here is where the 2025 study develops a significant methodological problem that, to my knowledge, has not been publicly identified.

The study found that dogs receiving CBD were on average three years older than dogs not receiving CBD. The conditions most strongly associated with CBD use were dementia at 18.2%, osteoarthritis at 12.5%, and cancer at 10%. In other words, the dogs in this study who were given CBD were disproportionately older, more unwell, and more likely to be in significant chronic pain.

Now consider: does CBD relieve pain in dogs? Yes.

The evidence here is considerably stronger than the evidence for CBD and aggression directly.

A 2025 randomised controlled trial found a CBD-based supplement significantly reduced pain, inflammatory markers, and oxidative stress in dogs with severe osteoarthritis.

A 2021 Cornell University prospective double-blind crossover study of 23 dogs found CBD measurably improved osteoarthritis-associated pain on objective gait analysis.

A 2024 randomised trial found CBD plus krill oil produced significantly better pain and stiffness scores than placebo in dogs with stifle osteoarthritis.

So. CBD reduces pain. Pain causes aggression.

The dogs in the 2025 study were predominantly older dogs with pain-associated conditions. And the study found aggression reduced over time in dogs receiving CBD.

Is the aggression reducing because CBD is acting on aggression pathways? Or is it reducing because CBD is relieving pain, and reduced pain is reducing aggression as a secondary consequence?

The study did not control for pain status.

The researchers did not ask whether the dogs were painful.

They observed aggression reduce and attributed it to CBD acting behaviourally. The most parsimonious explanation — that these are largely older, pain-affected dogs who feel better — was not examined.

This does not invalidate the finding. It reframes it considerably.

4. Seizure-Related Aggression

Canine idiopathic epilepsy affects an estimated 0.5 to 5.7 percent of the dog population and is the most common chronic neurological condition in dogs. Research shows that dogs with idiopathic epilepsy have significantly higher rates of fear, anxiety, and aggression compared to neurotypical dogs.

This manifests across three distinct phases.

Ictal aggression occurs during the seizure event itself, where abnormal neural firing can produce aggressive behaviour as part of the seizure semiology. Postictal aggression occurs in the recovery phase immediately following a seizure.

A study of 87 dogs found post-ictal signs in over 90 percent, with aggression reported in 17.7 percent. The postictal phase can last minutes to days, and its combined impact on quality of life has been shown in owner surveys to exceed the seizure itself.

Dogs in this phase are disoriented, potentially temporarily deaf or blind, and in a state of profound neurological disruption.

Aggression in this context is not a behavioural problem. It is a neurological event.

Interictal aggression — between seizures — is perhaps the most insidious.

Dogs with idiopathic epilepsy show elevated fear and aggression as a baseline state, not just in proximity to seizure events. This is now understood to reflect the broader neurological impact of the condition on behavioural regulation.

There is also rage syndrome, worth addressing carefully because it is frequently misunderstood. Rage syndrome — also known as episodic dyscontrol or limbic epilepsy — is a rare seizure disorder characterised by explosive, sudden aggression that is neurological rather than behavioural in origin.

The dog appears glassy-eyed, enters a dissociated trance-like state, and may attack without warning or apparent trigger.

It is most associated historically with English Springer Spaniels and English Cocker Spaniels, and is treated with anticonvulsants. It is also, importantly, frequently misdiagnosed — the term has been applied loosely to all sudden-onset aggression in spaniels for decades, when the true incidence of the neurological condition is rare.

A dog showing sudden aggression is far more likely to be in pain, frightened, or thyroid-compromised than to have rage syndrome. The label should not be the first port of call.

Now — and this is the critical point. Does CBD affect seizure activity in dogs?

Yes. Multiple randomised controlled trials say so.

A 2023 Colorado State University double-blind crossover study of 51 dogs found a 24.1 percent reduction in seizure days at 9mg/kg compared to a 5.8 percent increase in the placebo group.

A 2019 trial found a 33 percent median reduction in seizure frequency.

A 2025 systematic review examining all qualifying canine RCTs confirmed all three studies showed reduction in seizure frequency during CBD treatment.

If CBD reduces seizure frequency in dogs with idiopathic epilepsy, it would logically reduce all three phases of seizure-related aggression as a downstream consequence.

The 2025 Dog Aging Project study did not identify or separate epileptic dogs from its population. If a meaningful subset of the older, unwell dogs receiving CBD were also epileptic — and given the prevalence of epilepsy in the dog population, that is not improbable — then reduced seizure activity may be a third confounding explanation for the observed reduction in aggression.

The study cannot answer this question. It was not designed to.

5. Thyroid-Related Aggression

Hypothyroidism reduces serotonin turnover in the central nervous system via the same prefrontal pathway that underpins impulse control and aggression regulation.

It has been estimated to account for approximately 1.7 percent of aggressive behaviours in dogs — and critically, the behavioural signs can precede the physical signs by months or years.

A previously even-tempered dog becomes suddenly and unpredictably aggressive, with no obvious environmental trigger, before any of the classical hypothyroid presentations — lethargy, weight gain, coat changes — have appeared.

The evidence base is contested.

A controlled comparison of 31 aggressive dogs and 31 non-aggressive dogs found no significant differences in standard thyroid markers. But thyroglobulin autoantibodies — indicators of early thyroiditis — were elevated in the aggressive group, suggesting subclinical thyroid dysfunction may play a role even when standard tests appear normal.

For the CBD question: CBD has no known mechanism of action on thyroid function. If a dog's aggression is rooted in thyroid dysregulation, CBD will not address the cause. Thyroid supplementation might.

This is another reason why the blanket application of CBD to any aggressive dog — without clinical investigation of the underlying cause — is not sound practice.

6. Cognitive Dysfunction and Neurological Decline

The relationship between frontal lobe function and impulse control is direct.

As the prefrontal cortex degrades — whether through age-related cognitive dysfunction, inflammatory neurological disease, or neoplasia — its capacity to apply top-down inhibitory control over the aggression circuits declines with it.

Dogs with canine cognitive dysfunction frequently show what owners describe as personality change — irritability, reduced tolerance, snapping that was previously absent.

This matters for the 2025 study because 18.2 percent of the CBD-receiving dogs had dementia.

There is emerging evidence that CBD has neuroprotective and anti-inflammatory properties relevant to cognitive decline.

A 2025 PLOS One study found CBD improved learning and memory deficits and reduced anxiety in aged mice, with reduced oxidative stress as the proposed mechanism.

If CBD is modestly preserving prefrontal function in cognitively declining dogs, it may be maintaining their inhibitory capacity for longer — and reducing aggression as a consequence.

Again: not a direct effect on aggression. A secondary effect of addressing an underlying condition.

7. Learned Aggression

The one that CBD cannot touch, regardless of pathway or dosage.

Us dogs are extraordinarily good learners, (I can speak for myself on this one because I am well smart).

A dog that has discovered aggression works — that it reliably creates space, ends uncomfortable interactions, or obtains resources — has learned a strategy.

That strategy is maintained by its consequences. It is not mediated by fear, pain, neurological dysfunction, or hormonal imbalance. It is operant behaviour, shaped by the environment.

No pharmacological intervention addresses learned behaviour. Training and carefully structured behaviour modification are the only tools. A dog whose aggression is learned will not become less aggressive because its owner has added CBD oil to its dinner. It will become less aggressive when its learning history changes.

The failure to distinguish between pathological and learned aggression when discussing CBD is, in Percy's considered view, one of the more significant gaps in the public conversation about this topic.

PART THREE: THE METHODOLOGICAL PROBLEM STATED PLAINLY

Let me be direct...

The 2025 Dog Aging Project study found that CBD reduces aggression in a population of dogs that was predominantly older, in chronic pain, more likely to be epileptic, and more likely to be cognitively declining.

CBD has clinical evidence for pain relief, seizure reduction, and possible neuroprotective effects.

The most parsimonious (now that's a long word) explanation for the aggression finding may therefore be: CBD is addressing the underlying medical drivers in an older, unwell population, and aggression is reducing as a secondary consequence.

That is a genuinely interesting finding. But it tells us something quite different from the headline conclusion that CBD reduces aggression in dogs.

It does not tell us whether CBD would affect aggression in a younger, neurologically intact, non-painful dog whose aggression is rooted in fear, frustration, or learning.

It does not tell us whether CBD supports impulse control or frustration tolerance.

It does not tell us whether it might support the conditions under which behaviour modification work becomes more accessible — an extraordinary question with real implications for practitioners like Dog Smart that nobody has yet thought to ask.

These questions have not been studied.

The research to answer them does not exist.

The science is interesting and early.

The headlines are ahead of the evidence.

PART FOUR: THE LAW

Briefly, clearly, and without judgment.

In 2018, the UK Veterinary Medicines Directorate ruled that CBD products for animals are veterinary medicines requiring marketing authorisation before they can be sold or supplied for use on animals in the UK.

No CBD products have been granted that authorisation.

Administering CBD to a dog without a veterinary prescription is technically an offence under the Veterinary Medicines Regulations.

There is a legal route.

A veterinary surgeon can prescribe a human-authorised CBD product under the prescribing cascade. This is at individual veterinary discretion, is not common practice, and requires a clinical consultation.

Many UK owners are already using CBD products on their dogs, often bought online as human supplements, and doing so without awareness that this sits outside the legal framework.

The science is moving faster than the regulation. The enthusiasm is running well ahead of both.

PART FIVE: THE CONTAMINATION RISK THAT ALMOST NOBODY MENTIONS

I have left this until last because I consider it the most practically important point in this entire investigation.

Hemp — the plant from which CBD is extracted — is a hyperaccumulator.

This is not contested.

Hemp actively draws substances from the soil through its roots and concentrates them in its plant tissue.

This property is so well documented that hemp has been deliberately planted at Chernobyl to extract radioactive isotopes, and on Italian farmland contaminated by industrial dioxin from a neighbouring steel plant, specifically because of its capacity to pull toxins from the ground.

The metals hemp can accumulate include cadmium, lead, arsenic, and chromium.

A 2024 peer-reviewed study confirmed directly that the safety of any hemp-derived product must be assessed for heavy metal contamination as a matter of course.

A 2022 US analysis of commercially available CBD products found low-level contamination with heavy metals and phthalates was pervasive across the market. The same study found significant discrepancy between the CBD potency stated on product labels and the amount actually measured — meaning consumers frequently cannot know the dose they are administering.

For dogs — smaller animals, more sensitive to toxic accumulation, given a supplement daily and consistently — this is not a small concern.

The question of where the hemp was grown, what the history of that soil was, whether the crop was specifically cultivated for clean consumption rather than industrial purposes, and whether the finished product has been independently third-party tested for contaminants is not optional due diligence.

It is the minimum standard of care.

The market does not make these distinctions obvious. Many products do not provide this information.

A well-sourced, verified, third-party tested product from clean agricultural land is a fundamentally different proposition to an unverified oil of unknown provenance. The price difference between them is often less than the owner assumes.

PERCY'S CONCLUSION

Aggression in dogs is not a single condition with a single cause and a single treatment pathway.

It is a constellation of at least seven distinct presentations — fear, frustration, pain, seizure activity, thyroid dysfunction, neurological decline, and learned behaviour — each with a different neurological mechanism, a different prognosis, and a different response to any given intervention.

The CBD and aggression data is real.

The signal has replicated.

But the population of dogs in the primary study was old, medically complex, and disproportionately affected by conditions for which CBD has clinical evidence — pain relief, seizure reduction, possible neuroprotection.

The aggression reduction may be a secondary consequence of addressing those conditions rather than a direct effect on aggression itself. That interpretation was not tested.

The question of whether CBD modulates frustration tolerance, impulse control, or the conditions under which behaviour modification becomes more effective has never been asked in a canine population.

Given what human neuroscience tells us about the endocannabinoid system and the prefrontal cortex, it deserves to be.

In the United Kingdom, using CBD on your dog without a veterinary prescription is technically an offence. Many owners do not know this.

The hemp plant's capacity to accumulate heavy metals from contaminated soil represents a genuine safety risk in unverified products. Most owners do not know this either.

The science is fascinating and early.

The regulation has not caught up.

The market is operating ahead of both.

And the questions that would actually tell us something useful — which dogs, which aggression type, which mechanism, at what dose, from what source — are largely unasked.

That is the story. It is considerably more interesting than the headline.

Percy has used his voice for the good of dog. Now someone else needs to do the studies.

If anyone has a subject they want me to investigate, have a word with my dad because he still hasn`t got me my own mobile phone.

— Percy "TSO"

for Dog Smart Training & Behaviour

PRIMARY SOURCE

Conrow et al. (2025). Demographic features, health status, and behavioral changes associated with cannabidiol use in the Dog Aging Project. Frontiers in Veterinary Science, 12. DOI: 10.3389/fvets.2025.1666663

SUPPORTING SOURCES

Pain and aggression:

Camps et al. (2012). Pain-related aggression in dogs: 12 clinical cases. Journal of Veterinary Behavior, 7(2). DOI: 10.1016/j.jveb.2011.08.002

CBD and pain in dogs:

Gamble et al. (2018). Pharmacokinetics, Safety, and Clinical Efficacy of Cannabidiol Treatment in Osteoarthritic Dogs. Frontiers in Veterinary Science. https://pmc.ncbi.nlm.nih.gov/articles/PMC6065210/

CBD and seizures in dogs:

Rozental et al. (2023). The efficacy and safety of cannabidiol as adjunct treatment for drug-resistant idiopathic epilepsy in 51 dogs. Journal of Veterinary Internal Medicine. https://pmc.ncbi.nlm.nih.gov/articles/PMC10658598/

CBD and aggression in shelter dogs:

Corsetti et al. (2021). Cannabis sativa L. may reduce aggressive behaviour towards humans in shelter dogs. Scientific Reports. https://www.nature.com/articles/s41598-021-82439-2

CBD and inhibitory control in humans:

Rudroff et al. (2022). Differences in inhibitory control between CBD and THC users. Brain Sciences, 12(7). https://pmc.ncbi.nlm.nih.gov/articles/PMC9312972/

Seizure-related behaviour in dogs:

Frontiers in Veterinary Science (2023). Tools and techniques for classifying behaviours in canine epilepsy. https://www.frontiersin.org/.../fvets.2023.1211515/full

Hemp heavy metal contamination:

Heavy metal and phthalate contamination in CBD products (2022). PubMed. https://pubmed.ncbi.nlm.nih.gov/35987236/

UK legal position:

VMD Statement on CBD as veterinary medicine (2018): https://www.gov.uk/.../vmd-statement-on-veterinary...