Hemp & CBD Side Effects in Dogs: What the Studies Actually Found

Written by Marc Brannigan, Co-Founder & CEO of HempMy Pet.

Most articles about hemp side effects in dogs say some version of "it's usually safe, but talk to your vet." That is true, and it is not much help when you are standing in the kitchen holding a dropper and wondering what you are actually risking.

So this page does something different. It goes to the published canine research and tells you what the numbers were — how many dogs, what dose, what changed, and whether it went back to normal. We make hemp products, so read us with that in mind. We have also put our own oil through a university-overseen clinical trial, which means we have had to look hard at our own safety data rather than someone else's.

First: Hemp Seed Oil and Hemp Extract Are Not the Same Thing

Almost every confused safety question traces back to this. Two very different products are sold as "hemp oil for dogs."

• Hemp seed oil is pressed from the seed. It contains essentially no cannabinoids — no CBD, no THC. It is a nutritional oil, valued for its omega fatty acids. Its safety profile is basically that of any dietary fat: give too much and you may see loose stool or, over time, unwanted weight.
• Full-spectrum hemp extract is made from the flower and leaf. It contains CBD along with minor cannabinoids like CBG and CBC and the plant's natural terpenes. This is the one the research below is about, and the one with a real pharmacology worth understanding.

Our tinctures are full-spectrum hemp extract suspended in a carrier — hemp seed oil, coconut oil, or olive oil depending on the product. So they are both. If you want the distinction in more depth, we wrote a whole piece on hemp oil vs CBD oil for dogs, and there is a definition of full-spectrum hemp extract in our encyclopedia.

When someone says "hemp gave my dog diarrhea," it matters enormously which of these two they gave, and how much.

The Side Effects Actually Reported in Dogs

Pulled from the published veterinary literature and from what owners consistently report:

Effect	How common	What to do
Drowsiness or sedation	The most commonly reported effect	Usually means the serving is slightly high. Reduce it.
Loose stool or soft stool	Fairly common, often carrier-related	Reduce the amount; give with a meal rather than on an empty stomach.
Increased appetite	Noted by owners in Cornell's summary	Usually harmless. Watch weight over months.
Dry mouth / more drinking	Occasional	Make sure water is available. Not a reason to stop.
Hypersalivation (drooling)	Sporadic in one 90-day study; not classed as an adverse event	Often a taste reaction. Try mixing into food.
Raised alkaline phosphatase (ALP)	The consistent lab finding — see below	Worth a conversation with your vet, especially long term.

Notably, in the 90-day safety study described below, there was no vomiting, diarrhea or somnolence recorded across the whole dosing period.

The Liver Enzyme Question — What the Numbers Actually Say

This is the question that worries people most, and it is the one nearly every article answers vaguely. Here is the specific research.

Cornell, 2018 — the finding that started the conversation

In the Cornell osteoarthritis trial published in Frontiers in Veterinary Science, 16 dogs received 2 mg/kg of CBD every 12 hours for four weeks. The researchers reported a statistically significant increase in serum alkaline phosphatase during CBD treatment (p < 0.01), seen in nine of the sixteen dogs.

Two things are worth holding together. First, the authors also wrote that no side effects were reported by owners — the dogs seemed fine; the change showed up on bloodwork. Second, the authors themselves noted that a rise in ALP is "fairly sensitive for hepatobiliary changes in this age group, but not specific" — meaning it flags that something is happening in the liver or biliary system without telling you what, or whether it matters. They recommended monitoring liver values during use, pending longer studies.

2024 — a longer, larger look

Those longer studies have since been done. A 90-day safety study in Frontiers in Veterinary Science dosed 32 healthy beagles at 5 mg of total cannabinoids per kg per day — a substantially higher daily amount than most owners give — across three formulations, with a 14-day recovery period afterwards.

ALP did move, most notably in the CBD-only group. But the values stayed within the laboratory's normal reference range, and where a value did rise it decreased at each subsequent evaluation. The authors concluded that cannabinoids "were well tolerated when healthy male and female beagles were dosed for 90 consecutive days."

So what does that mean for your dog?

The honest reading: hemp appears to nudge a liver enzyme in a meaningful fraction of dogs, the effect is generally mild and reversible, and it has not been shown to cause liver damage at the doses studied. It is a monitor-it finding, not a don't-do-it finding.

What that means practically is simple. If your dog is going to take hemp long term, ask your vet for a baseline blood panel before you start and a re-check after a few months. That is a cheap piece of information and it turns an open question into a known one. It matters more if your dog already has liver disease, is older, or takes other medications.

Drug Interactions: The Part That Actually Matters

If there is one genuine risk in this article, it is this one — and it follows directly from the enzyme finding above.

As Cornell's Riney Canine Health Center explains, CBD affects cytochrome P450 enzymes and alkaline phosphatase — both involved in metabolising many medications. In plain terms: hemp can change how fast your dog's body processes a drug it is already taking. The drug does not become dangerous because hemp is dangerous; it becomes unpredictable because the clearance rate moved.

This is why "check with your vet" is not a legal disclaimer on this page. It is the actual advice. Your veterinarian knows what else is in your dog, and we do not.

It is worth saying that hemp alongside medication is not automatically a problem. In our own 90-day canine trial, dogs stayed on their existing prescriptions while hemp oil was added, and every medication change was directed by the supervising veterinary pain specialist. That is the model to copy: supervised, not improvised.

Signs You Have Given Too Much

Hemp at sensible servings is non-intoxicating. Too much is uncomfortable rather than dangerous, and the signs are recognisable:

• Unusual sleepiness, or a dog that seems "flat"
• Wobbliness or unsteadiness on their feet
• Loose stool
• Low appetite for a meal or two

These typically pass on their own within a few hours to a day. Reduce the serving next time rather than stopping altogether.

A genuinely different situation: if your dog has eaten a cannabis product containing THC — an edible, a vape cartridge, a stash — that is not a hemp side effect, it is a toxicity, and it needs a vet or a poison line immediately. Signs include severe wobbliness, dribbling urine, sensitivity to light and sound, and dilated pupils. We cover the distinction on our THC page. Hemp products under 0.3% THC do not do this.

How to Lower the Risk

Start low and go slow

Most side effects are dose-related. Begin at the low end for your dog's weight and hold there for a week before adjusting. Our serving guide works from body weight, and each product page carries its own chart.

Read the certificate of analysis

This is the single highest-leverage safety habit, and most owners skip it. Cornell's summary of the market found heavy metal contamination in four of 29 CBD products evaluated, and only ten products containing cannabinoid concentrations within 10% of what the label claimed. A product that contains far more or far less than it says is a safety problem before you have given a single drop. Every one of our batches is third-party tested and the results are on our lab results page; if you are shopping elsewhere, learn to read a COA.

Give it with food

Cannabinoids are fat-soluble. Giving hemp with a meal is gentler on the stomach and helps absorption.

Watch the first two weeks

Most of what you will learn about how your dog responds happens early. Note sleep, stool, appetite and energy. If something changes, you will know what caused it.

The Carrier Oil Is Part of the Side Effect Picture

This rarely gets mentioned, and it explains a lot of the loose-stool reports. A hemp tincture is cannabinoid extract suspended in a carrier oil, and the carrier is most of what your dog is actually swallowing. Different carriers behave differently in a dog's gut.

Carrier	Fat profile	Tolerability notes
Coconut oil (MCT)	Largely saturated, medium-chain	Absorbs quickly. The carrier most associated with loose stool if the amount jumps too fast — MCTs are famous for it in humans too. Start low and it is rarely a problem.
Hemp seed oil	Over 80% polyunsaturated	Adds omega fatty acids. Because it is highly unsaturated it is the least shelf-stable of the three — refrigerate after opening. Cold thickens it, so stand the bottle out for a minute before dosing.
Olive oil	Mostly monounsaturated	The gentlest and most stable of the three, and palatable for large dogs and horses. A cool dark cupboard is fine.

If your dog got loose stool on one product, it is genuinely worth trying a different carrier before concluding hemp does not suit them. In our experience that solves it more often than not. It is also a reason to give the tincture with food rather than on an empty stomach — the meal slows everything down.

Telling a Side Effect From a Coincidence

Dogs have off days. The hard part of judging any supplement is knowing whether what you are seeing is the product or the week.

A simple two-week log settles it, and costs nothing. Before your first serving, write down four things: how your dog sleeps, what their stool looks like, how much they are eating, and roughly how they move — the stairs, the sofa, the last ten minutes of a walk. Then note the same four every few days.

Two rules make the log useful. Change one thing at a time — do not start hemp the same week you switch food or begin a new medication, or you will never know which did what. And if you see something you do not like, lower the serving rather than stopping outright; if it clears, you have found your dose, and if it does not, hemp probably was not the cause.

Almost everything worth knowing about how your individual dog responds shows up in those first two weeks.

When to Call Your Veterinarian

• Before starting, if your dog takes any prescription medication — particularly anything for seizures, pain, or behaviour
• Before starting, if your dog has known liver or kidney disease
• If loose stool or lethargy lasts more than about 48 hours after you have reduced the amount
• If your dog is on hemp long term and has not had bloodwork in a year
• Immediately, if you suspect they have eaten a THC product

What We Still Do Not Know

We would rather say this plainly than let you find it out later.

Long-term canine safety data now extends to about 90 days in controlled studies. Multi-year data does not really exist yet. There is little good evidence on hemp in pregnant or nursing dogs, or in puppies, which is why the sensible position is to avoid it in all three. Studies use specific, measured products; the shelf does not, which is why the COA point above carries so much weight. And the FDA has not approved hemp products for any use in animals, so nobody — us included — can tell you hemp treats or cures a condition.

Puppies, Seniors, Cats and Horses

Puppies: not enough evidence. We do not recommend it for growing dogs.

Senior dogs: the most common users, and the group most likely to be on other medications — so the interaction conversation matters most here. Our joint and mobility page covers what our clinical trial found in older dogs.

Cats: cats metabolise cannabinoids differently from dogs, so canine guidance does not transfer. See hemp serving sizes for cats and cat safety.

Horses: different again, with competition-rule implications on top. Our equine research page covers it.

Frequently Asked Questions

Can I give my dog hemp oil every day?
Yes — daily use is how hemp is generally given, and consistency tends to matter more than any single serving. The published safety studies dosed daily for 90 consecutive days without clinically relevant problems. If your dog will be on it long term, ask your vet about periodic bloodwork.

Do vets recommend hemp for dogs?
It varies, and state rules on what a veterinarian may discuss vary too. Many are open to it and want to be told; veterinary institutions including Cornell are actively researching it. What nearly all of them agree on is that you should tell your vet your dog is taking it, because of the medication-interaction issue.

What is better for dogs, hemp oil or CBD oil?
They are usually the same thing under two names, which is exactly where the confusion starts. What matters is whether the product contains full-spectrum hemp extract (cannabinoids present) or only hemp seed oil (essentially none). Check the label for a cannabinoid amount in milligrams. If there isn't one, it is seed oil.

How long does it take for hemp oil to kick in for dogs?
Given as an oil directly by mouth, many owners notice something within about 30 to 60 minutes; treats take longer because they digest first. For ongoing support, judge it over one to two weeks of consistent use rather than a single dose. More detail on onset and duration.

Can a dog overdose on hemp oil?
Not in the life-threatening sense at the concentrations in pet products under 0.3% THC. Too much causes drowsiness, wobbliness and loose stool that resolve on their own. A THC-containing cannabis product is a different matter entirely and is a veterinary emergency.

Can I give my dog human CBD oil?
We would not. Human products are concentrated for a much larger body, may be flavoured with sweeteners including xylitol, which is toxic to dogs, and are not formulated with a pet's serving size in mind. Use a product made for the animal.

Does hemp oil damage a dog's liver?
There is no evidence that it does at studied doses. What the research shows is a rise in alkaline phosphatase in some dogs — mild, reversible, and within normal reference ranges in the 90-day study. It is a reason to monitor, not a reason to avoid.

Where Our Own Research Fits

We commissioned a 90-day clinical trial of our full-spectrum hemp oil in dogs with chronic joint discomfort, overseen by veterinary pain specialist Dr. Robin Downing with researchers from Colorado State University's College of Veterinary Medicine. Thirty-seven dogs were enrolled, 32 completed the study, and 30 of those 32 showed a benefit. It was published in the Journal of the American Holistic Veterinary Medical Association, and you can read the paper in full.

Per the journal's published disclosure, we supplied the oil and reimbursed clinic costs but had no input into the study's design or interpretation. That distinction is the reason the study is worth citing at all, and it is why we would rather tell you about an enzyme finding than leave you to discover it somewhere else.

If you want to see what we make and how it is tested, start with hemp for dogs, or read the clinical trials overview.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Always consult your veterinarian before starting any new supplement, especially if your dog is taking medication or has a health condition.