CBD and Your Dog's Medications: What the Canine Research Actually Shows

If your dog is on medication and you are wondering whether hemp oil is safe to add, you have probably found two kinds of answers online: supplement brands saying it is fine, and pet-health sites listing a long column of drugs to avoid. Almost none of them tell you where their list came from.

We went looking. The honest answer is more interesting than either version — and it is not what we expected before reading the papers.

Below is the mechanism in plain English, what happened when it was tested in real dogs, the drug-by-drug picture, and the practical part: how to introduce hemp to a dog who is already on something, and what to watch for.

How CBD Could Interact With a Medication at All

Your dog's liver breaks down most drugs using a family of enzymes called cytochrome P450, usually shortened to CYP. Think of them as a set of doorways. Each drug leaves the body through a particular doorway, and if two substances want the same doorway at the same time, one can back up — leaving more of it circulating for longer than the prescribing vet intended.

CBD uses those doorways too. That is the whole basis of the interaction concern, and it is a legitimate one.

Here is the problem with how it gets reported. In humans, CBD is a known inhibitor of an enzyme called CYP3A4, and CYP3A4 handles an enormous share of human prescriptions. That single fact is where nearly every "CBD drug interactions in dogs" list ultimately comes from. But dogs are not small people. They have their own set of CYP enzymes with their own names — CYP1A2, CYP2B11, CYP2C21, CYP2D15, CYP3A12 — and they do not map onto the human ones neatly.

Which raises the obvious question: has anyone checked in dogs?

What the Canine Studies Actually Found

The dog-specific enzyme work

In 2024, a team led by Michael Court published the first real look at this in the Journal of Veterinary Pharmacology and Therapeutics — a preliminary in vitro evaluation using dog liver microsomes and recombinant canine enzymes. Three findings matter for owners:

• The human CYP3A4 story did not transfer. Neither CBD nor CBDA meaningfully inhibited CYP3A12 — the canine enzyme closest in role to human CYP3A4 — at the concentrations tested. The single most-cited reason to fear CBD interactions in dogs did not reproduce in dog tissue.
• One drug came up specifically: tramadol. CBD and CBDA both inhibited the enzymes dogs use to process tramadol (CYP2B11, and CYP2D15 for CBDA), at concentrations low enough to be worth taking seriously. If your dog is on tramadol, this is the interaction to raise with your vet by name — and our guide to tramadol for dogs covers why the drug may be doing less than you think in the first place.
• Phenobarbital may lower CBD, not the reverse. Phenobarbital induces CYP2C21, one of the two enzymes that clears CBD in dogs. So the likely direction of that interaction is a dog on phenobarbital clearing CBD faster — the opposite of what most articles imply.

CBD and CBDA were also not substrates or inhibitors of canine P-glycoprotein, a transporter that matters for some drugs. And hemp extracts behaved identically to pure cannabinoids, which is worth knowing if you have read that "whole plant" products are somehow less predictable.

The authors were careful, and so are we: this was in vitro — cells and enzymes in a lab, not live dogs — and they explicitly called for in vivo confirmation. A test tube is a hypothesis, not a conclusion.

What happened in live dogs

Two studies took the next step, and both looked at the drug most people would worry about most: phenobarbital, an anticonvulsant with a narrow margin between a working dose and a toxic one.

Doran and colleagues (2021), American Journal of Veterinary Research — a three-phase study in nine healthy Beagles giving CBD at 5, 10 and 20 mg/kg, phenobarbital alone, and both together. The conclusion was blunt: "No significant PK interactions were found between CBD and PB. Dose escalation of CBD or adjustment of PB in dogs is not recommended on the basis of findings of this study."

Rozental and colleagues (2023), Journal of Veterinary Internal Medicine — a double-blinded crossover trial in 51 dogs with drug-resistant epilepsy, nearly all of them on two or more antiseizure drugs, most commonly phenobarbital plus levetiracetam. CBD at 9 mg/kg/day for 12 weeks. On drug levels: no difference between CBD and placebo in the concentration of any antiseizure drug measured.

Read together, that is genuinely reassuring on the question owners actually ask. In dogs on the medication with the least room for error, adding CBD did not move the drug levels.

The Finding Brands Do Not Lead With

Both of those studies found something else, and it is the part worth your attention.

In the Rozental epilepsy trial, alkaline phosphatase (ALP) rose sharply — mean values went from 278 IU/L at baseline to 1,585 IU/L after three months on CBD. ALT rose too, from a mean of 64.4 to 114.5. Decreased appetite and vomiting were also more common during the CBD phase. In the Doran Beagle study, four of nine dogs showed increased ALP, and five showed hypoxia at the 10 to 20 mg/kg daily doses.

That sounds alarming out of context, so here is the context — and it is mostly about how much.

A separate six-month study by Logan and colleagues in Frontiers in Veterinary Science gave 40 healthy dogs either 4 mg/kg of CBD daily or a placebo. Eleven of the 20 CBD dogs (55%) had ALP above the reference range, and none of the placebo dogs did. But the rise was isolated — no other liver marker moved with it — and it correlated strongly (r > 0.9) with bone alkaline phosphatase rather than the liver kind, pointing at bone cell activity rather than liver injury. Every elevated value returned to baseline after a four-week washout, and the dogs stayed healthy throughout.

Three things follow from putting those studies side by side:

• Dose drives it. The dramatic numbers came from 9 mg/kg in epileptic dogs already on phenobarbital — a drug that raises ALP on its own. The mild, reversible, largely bone-derived picture came from 4 mg/kg in healthy dogs. For reference, the dogs in our own 90-day joint-comfort trial finished between 0.3 and 4.12 mg/kg twice daily, and we have put every dose used across all five published canine trials side by side so you can see where any product falls.
• An isolated ALP rise is not the same as liver damage — but distinguishing the two requires a blood panel, not a guess.
• It appears to reverse. In the study that tested for it, stopping brought the numbers back.

We went through the liver-enzyme literature study by study, including our own trial's numbers, in our guide to hemp and CBD side effects in dogs. The short version for this page: if your dog is on any medication the liver handles, baseline bloodwork before you start and a recheck a few weeks in is the single most useful thing you can do — far more useful than avoiding a drug on a list someone copied from a human pharmacology textbook.

Drug by Drug: Where to Pay Attention

Rather than an alphabetical list of thirty drugs, here is the same information sorted by what you would actually do about it. Every one of these is a conversation with your vet, not a decision to make alone.

Medication	What the concern actually is	What it means in practice
Tramadol	The one drug canine enzyme work flagged directly — CBD and CBDA inhibited the pathways dogs use to clear it	Name it to your vet specifically before adding hemp
Gabapentin	Additive drowsiness, not a drug-level problem	Start low; expect a sleepier dog in week one
Trazodone, benzodiazepines, opioids, sedating antihistamines	Additive drowsiness and wobbliness	Same — the effects stack, so introduce slowly
NSAIDs (carprofen/Rimadyl, meloxicam, deracoxib, firocoxib, grapiprant)	Both the NSAID and CBD load the liver; monitoring matters more here than anywhere	Baseline bloodwork, then recheck
Phenobarbital	Tested twice in dogs with no drug-level change — but it may clear CBD faster, and it raises ALP on its own	Do not adjust either dose yourself; monitor
Cyclosporine (Atopica), azole antifungals, chemotherapy agents	Narrow margin between working and toxic; not specifically studied with CBD in dogs	Vet decision before you start, not after
Prednisone, Apoquel, thyroid medication, most antibiotics, heartworm and flea preventives	No canine-specific interaction evidence either way	Tell your vet anyway; watch the first two weeks

Two notes on that table. First, "no evidence of an interaction" is not the same as "proven safe together" — most of these combinations have simply never been studied in dogs, and honest uncertainty is the correct position. Second, the antacid point that comes up on gabapentin pages is a real one but unrelated to hemp: antacids reduce gabapentin absorption, which is why vets often suggest separating those doses by about two hours.

Gabapentin — the one we have our own data on

This is the combination we get asked about most, partly because the advice online openly contradicts itself, and partly because it is the one place we have something to contribute rather than just cite.

Pharmacologically, gabapentin is a relatively low-drama partner. In dogs it is partly converted to N-methyl-gabapentin and partly excreted unchanged in urine — a 2023 review in Animals lays out the canine pharmacokinetics — so it does not compete for the same crowded doorway that worries people. The real issue is simpler and more practical: both gabapentin and hemp extract can make a dog drowsy, and given together that effect stacks. That is a reason to start at the low end and watch, not a reason to assume danger.

On what happens over time, our own trial is the most direct evidence we know of. In a 90-day study of 37 dogs with chronic joint discomfort overseen by veterinary pain specialist Dr. Robin Downing with researchers from Colorado State University, 23 of the dogs were taking gabapentin at enrollment. By the end, 10 had discontinued it entirely and 11 more had reduced their dose — every change made by that dog's own veterinarian at a scheduled reassessment, never by an owner. The 2023 Frontiers in Veterinary Science systematic review restates that finding independently.

What that is: an open-label pilot with no control group, in dogs on several therapies at once. What it is not: a promise about your dog. We go through the whole picture — including gabapentin's own side-effect profile and why stopping it abruptly is dangerous — in our guide to gabapentin for dogs and its side effects.

NSAIDs — the combination to be most careful with

If we had to pick one pairing to slow down on, it is hemp alongside a long-term NSAID like carprofen or meloxicam. Not because of a documented drug-level interaction — there isn't one published in dogs — but because both are processed by the liver, NSAIDs already carry their own monitoring recommendations, and the ALP signal above means you want to be able to tell which substance any change belongs to. That is only possible if you have a baseline.

Most dogs on a daily NSAID are on it for joint comfort, which is the same reason most owners come looking for hemp. If that describes your dog, our write-up on Rimadyl and carprofen side effects covers the liver question honestly, and our full guide to hemp and CBD oil for dogs with joint discomfort covers where each piece fits.

How to Introduce Hemp to a Dog Already on Medication

The practical part, in the order we would do it.

1. Tell your vet first, and name the product. Bring the actual bottle or the Certificate of Analysis. "CBD oil" tells them nothing; "full-spectrum hemp extract, 1000 mg per 30 ml, third-party tested, 0.3% THC or less" tells them what they need. Name tramadol, phenobarbital, cyclosporine or an NSAID specifically if your dog is on one.
2. Get baseline bloodwork. A standard chemistry panel before you start. This is the step people skip and the one that makes everything afterwards interpretable.
3. Start low and go slow — lower than you think. A widely used starting reference is 1 to 3 mg of CBD per 10 lb of body weight, once or twice daily, which is roughly 0.2 to 0.7 mg/kg. The studies showing the biggest liver-enzyme changes used 9 mg/kg. There is a lot of room below that. Each product page has its own serving chart by weight, since the right volume depends on the strength you choose.
4. Give it with food. Fat improves absorption and food reduces the chance of stomach upset, which was among the more common complaints in the epilepsy trial.
5. Keep the medication schedule exactly as prescribed. If you want to space hemp and a medication a couple of hours apart, that is reasonable and harmless — but do not shift, skip or reduce a prescription to make room for it.
6. Watch the first two weeks, and write things down. Sleepiness, steadiness on stairs, appetite, stool. A note on your phone beats memory when your vet asks.
7. Recheck bloodwork in four to eight weeks. Then at whatever interval your vet suggests. This is the whole game.
8. Never change a prescription yourself. Not the dose, not the timing, and above all not stopping — abruptly discontinuing gabapentin or an anticonvulsant can trigger withdrawal seizures.

Signs of a Possible Interaction

Most of what you would notice is an exaggerated version of the sedation each substance can cause on its own. Call your vet if you see:

• Sedation that is clearly deeper than the medication alone produced, or that is not easing after a week.
• Wobbliness or difficulty on stairs that is new since you added hemp.
• Loss of appetite, repeated vomiting, or diarrhea that persists past a couple of days.
• Yellowing of the gums or eyes, dark urine, or unusual lethargy — call the same day.
• Any change in seizure frequency in a dog with epilepsy.
• A medication that suddenly seems to be working differently than it did.

And a genuine emergency, unrelated to interactions but worth knowing: if your dog may have eaten a THC product — an edible, a vape cartridge, a joint — that is marijuana toxicity, not a hemp question, and it needs a vet now.

Questions Worth Asking Your Vet

• Given what my dog is on, is there anything here you would specifically not combine?
• Can we run a chemistry panel before I start, and when would you want to recheck it?
• Is my dog's medication one the liver clears, or one the kidneys handle?
• If my dog's ALP goes up but nothing else does, how would you interpret that?
• Is there anything else in the plan — weight, activity, joint support — that could carry more of the load?

If your vet is uncomfortable discussing hemp at all, that is worth knowing too. The American Kennel Club has a practical guide to raising it, and Cornell's Riney Canine Health Center has a level-headed overview you can bring with you.

Frequently Asked Questions

Can CBD interact with my dog's medications?
It can, in principle — CBD is processed by the same liver enzyme family that clears most drugs. But when researchers tested it in live dogs, the drug-level interactions largely did not appear. Two studies found no change in phenobarbital or other antiseizure drug concentrations. The more consistent finding is a rise in the liver enzyme ALP, which is why bloodwork matters more than a list of forbidden drugs.

Which medication is the biggest concern with CBD in dogs?
Tramadol is the one canine enzyme research flagged by name — CBD and CBDA inhibited the pathways dogs use to clear it in laboratory testing. Long-term NSAIDs like carprofen deserve care too, not because of a documented interaction but because both load the liver, so you want baseline bloodwork to tell changes apart.

Can my dog take CBD and gabapentin together?
That is a question for your veterinarian, and the main consideration is additive drowsiness rather than a drug-level problem — gabapentin in dogs is partly excreted unchanged in urine. In the 90-day trial that examined the combination directly under veterinary supervision, 21 of 23 dogs on gabapentin were able to reduce or discontinue it. Never adjust a prescription yourself.

Does CBD affect liver enzymes in dogs?
Yes, and this is the best-documented effect. ALP rises in a meaningful share of dogs, and it tracks with dose. In healthy dogs at 4 mg/kg daily for six months, 55% had elevated ALP, but it was isolated, correlated with bone rather than liver origin, and returned to baseline after a four-week washout. At 9 mg/kg in epileptic dogs also on phenobarbital, the rise was far larger. Baseline and follow-up bloodwork is how you tell which situation you are in.

How long should I wait between giving CBD and medication?
Spacing them a couple of hours apart is reasonable and harmless, and some owners prefer it. There is no canine evidence that a specific gap is required. What matters far more is keeping the prescription exactly on its schedule and starting hemp at a low serving.

Does the human CYP3A4 warning apply to dogs?
Apparently not, which surprised us. Nearly every interaction list for dogs traces back to CBD inhibiting human CYP3A4. When tested against the canine equivalent, CYP3A12, neither CBD nor CBDA inhibited it meaningfully. That was in vitro and needs live-dog confirmation, but it is a good reason to treat human-derived lists with caution.

Should I stop my dog's medication if the hemp seems to be helping?
No — not on your own, and never abruptly. Stopping gabapentin or an anticonvulsant suddenly can cause withdrawal seizures. In the trial where dogs did reduce gabapentin, every change was made by that dog's own veterinarian at a scheduled reassessment. If less medication is your goal, that is a reasonable goal to bring to your vet and a schedule for them to manage.

Is full-spectrum hemp more likely to interact than CBD isolate?
The canine enzyme study tested both pure cannabinoids and cannabinoid-rich hemp extracts and reported identical results, so there is no evidence full-spectrum behaves less predictably. What does matter is knowing what is actually in the bottle, which is what a third-party Certificate of Analysis is for.

If joint comfort is what brought you here, our hip and joint mobility range and the broader hemp oil for dogs collection use the same full-spectrum oil that was studied in the trial above — grown on our own Colorado farm, third-party tested every batch, with the endocannabinoid system explained in our encyclopedia if you want the biology. Bring it to your vet alongside everything else your dog takes.

How We Sourced This Article

Every claim above traces to one of these. We have linked each one in the text so you can check it yourself.

• Court MH, et al. Cannabidiol and cannabidiolic acid: Preliminary in vitro evaluation of metabolism and drug–drug interactions involving canine cytochrome P-450, UDP-glucuronosyltransferase, and P-glycoprotein. Journal of Veterinary Pharmacology and Therapeutics. 2024;47:1–13. PubMed. The source for the CYP1A2/CYP2C21, tramadol, CYP3A12 and P-glycoprotein findings. In vitro; the authors call for in vivo confirmation.
• Doran CE, McGrath S, Bartner LR, et al. Drug-drug interaction between cannabidiol and phenobarbital in healthy dogs. American Journal of Veterinary Research. 2021;83:86–94. PubMed. Nine Beagles; no pharmacokinetic interaction found; ALP rise in four dogs and hypoxia in five at 10–20 mg/kg/day.
• Rozental AJ, Weisbeck BG, Corsato Alvarenga I, et al. The efficacy and safety of cannabidiol as adjunct treatment for drug-resistant idiopathic epilepsy in 51 dogs: A double-blinded crossover study. Journal of Veterinary Internal Medicine. 2023;37:2291–2300. PubMed. Source for the unchanged antiseizure drug concentrations and for the ALP and ALT figures at 9 mg/kg.
• Logan DW, et al. Long-term daily feeding of cannabidiol is well-tolerated by healthy dogs. Frontiers in Veterinary Science. 2022;9:977457. Source for the six-month, 4 mg/kg ALP data and the bone-ALP correlation.
• Di Cesare F, Negro V, Ravasio G, et al. Gabapentin: Clinical Use and Pharmacokinetics in Dogs, Cats, and Horses. Animals. 2023;13(12):2045. PubMed. Source for how dogs metabolise and excrete gabapentin.
• Kogan L, Hellyer P, Downing R. The Use of Cannabidiol-Rich Hemp Oil Extract to Treat Canine Osteoarthritis-Related Pain: A Pilot Study. Journal of the American Holistic Veterinary Medical Association. 2020;58:35–45. DOI 10.56641/UPRM3253. Full PDF. Our disclosure: HempMy Pet supplied the hemp extract and reimbursed clinic costs. Per the journal, we had no input into study design or interpretation.
• Frontiers in Veterinary Science (2023) — Pharmacokinetics, efficacy, and safety of cannabidiol in dogs: an update of current knowledge. An independent systematic review that restates the gabapentin finding above.
• VCA Animal Hospitals — Gabapentin and oral cyclosporine monographs, for each drug's own documented cautions.

If you find something here that conflicts with your veterinarian or with a source we have missed, email us at support@hempmypet.com and we will correct it. We update this article as new canine research is published.

These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. This article is educational and is not veterinary advice. Never start, stop, or change your dog's prescription medication without your veterinarian.