CBD safety and side effects in dogs

What does the research say about CBD safety in dogs?

The foundational safety trial is a 2018 randomized, placebo-controlled study at Cornell University, published in Frontiers in Veterinary Science (https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2018.00165/full). Twenty-two dogs with osteoarthritis received CBD for four weeks. The study found no adverse clinical effects. Bloodwork showed kidney values and liver function remained within normal ranges, and no dogs developed clinical signs of illness. The only laboratory finding was a dose-dependent increase in alkaline phosphatase (ALP), a liver enzyme, which resolved after CBD was stopped.

Longer trials confirm these findings. A 2022 study followed 40 dogs for six months, with 20 receiving CBD once daily and 20 receiving placebo (https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.977457/full). The CBD group showed no serious adverse events. A 2024 trial tracked 18 beagle dogs receiving CBD daily for 36 weeks and reported it was well tolerated, with no clinically significant changes in behavior, body weight, or organ function (https://pmc.ncbi.nlm.nih.gov/articles/PMC10800185/). A separate 2024 safety study tested CBD in 24 beagle dogs over 90 days and found it well tolerated (https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1349590/full).

A 2023 systematic review in Frontiers in Veterinary Science summarized multiple pharmacokinetic and safety studies and concluded that CBD is generally safe in dogs at the doses studied, with side effects that are mild and manageable.

What side effects do dogs experience on CBD?

The most common side effects are sedation, increased thirst, temporary diarrhea, and reduced appetite. These effects are dose-dependent and typically resolve when the dose is lowered.

Sedation or lethargy appears most often at doses higher than needed for the condition being treated. If your dog seems unusually tired or slow to respond, reduce the dose.

Increased thirst occurs because CBD can cause mild dry mouth, leading dogs to drink more water. This is not harmful.

Temporary diarrhea happens especially when CBD is first introduced, or when the carrier oil (usually MCT or hemp seed oil) is added too quickly to the diet. Starting at a low dose and increasing gradually reduces this risk.

Reduced appetite or nausea can occur at high doses. Counterintuitively, the same compound used to support appetite at moderate doses may suppress it when the dose climbs too high. Lowering the dose resolves this.

What is the alkaline phosphatase elevation in dogs on CBD?

Many dogs on CBD show elevated alkaline phosphatase (ALP) on routine bloodwork. ALP is a liver enzyme, but it also originates from bone. Research suggests the elevation in dogs on CBD often includes bone-derived alkaline phosphatase (BALP), not just the liver form.

A 2022 study following dogs for six months found ALP elevations that were not accompanied by clinical signs of liver disease (https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.977457/full). The enzyme level typically plateaus by week eight and shows high individual variation. When CBD is stopped, ALP returns to baseline.

Elevated ALP without clinical signs does not indicate liver damage and does not require stopping CBD. However, dogs on long-term CBD should have ALP monitored as part of annual bloodwork. Dogs already on medications that affect the liver, such as phenobarbital or long-term NSAIDs, warrant closer monitoring. Talk to your vet if your dog is on other medications.

Can CBD interact with other medications my dog is taking?

Yes. CBD inhibits cytochrome P450 liver enzymes, specifically CYP1A2 and CYP2C21 pathways in dogs, which are responsible for metabolizing many pharmaceutical drugs. When CBD slows these enzymes, other drugs clear more slowly from the bloodstream, which can increase their effective concentration and lead to side effects or toxicity.

The interaction is most clinically significant with phenobarbital, a common anti-seizure medication. A 2022 study in the American Journal of Veterinary Research tested six healthy dogs and found that CBD increased phenobarbital blood levels (https://avmajournals.avma.org/view/journals/ajvr/83/1/ajvr.21.08.0120.xml). Dogs on phenobarbital who are given CBD require veterinary monitoring and may need a dose adjustment of the phenobarbital.

NSAIDs such as carprofen (Rimadyl), grapiprant (Galliprant), and meloxicam may also interact, though the effect is less dramatic. The combination can increase the risk of gastrointestinal upset. Monitor your dog for vomiting, diarrhea, or loss of appetite.

Cardiac medications and chemotherapy agents also metabolize through CYP450 pathways. Always consult your veterinarian or veterinary specialist before adding CBD if your dog is on heart medication or undergoing cancer treatment.

What is THC toxicity and how is it different from CBD?

THC (tetrahydrocannabinol) is the psychoactive compound in cannabis and is toxic to dogs. Dogs have a higher density of CB1 receptors in the cerebellum and brainstem compared to humans, making them more susceptible to THC toxicity, particularly ataxia and loss of coordination.

Clinical signs of THC toxicity in dogs include stumbling or loss of coordination (ataxia), glassy eyes with dilated pupils, urinary incontinence, tremors, extreme lethargy or unresponsiveness, and vomiting. Signs range from mild to moderate depending on the amount consumed. Deaths from THC ingestion are rare, but the toxicity is distressing and requires veterinary treatment in severe cases.

CBD itself is not THC and does not cause these signs. However, some CBD products contain THC, either because they are full-spectrum formulations or because of contamination or mislabeling. The risk of THC exposure comes from the product, not from CBD as a compound. Use only broad-spectrum or CBD isolate products with a certificate of analysis (COA) from a third-party laboratory showing 0% THC.

How should I choose a safe CBD product for my dog?

Look for a product with a certificate of analysis (COA) from an independent laboratory, showing cannabinoid content and confirming 0% THC. The COA should also screen for pesticides, heavy metals, and microbial contaminants.

Avoid products that contain xylitol, an artificial sweetener that is highly toxic to dogs. Check the ingredient list carefully. Human CBD products are more likely to contain xylitol, flavorings, or other additives not safe for dogs.

Choose a product labeled for dogs and start at the low end of the suggested range. Increase slowly over several days and watch for side effects. Check with your vet for guidance on dosing.

Check your state's laws regarding CBD and hemp-derived products, as regulations vary.

When should I call the vet?

See your vet if your dog shows signs of severe sedation, loss of coordination, tremors, vomiting that does not resolve, or urinary incontinence after receiving CBD. These signs may indicate THC contamination or an interaction with another medication.

Call your vet if your dog is on phenobarbital, heart medication, or chemotherapy and you are considering adding CBD. Blood level monitoring or dose adjustments may be needed.

If your dog consumes a large amount of CBD oil, contact your vet. While serious toxicity is unlikely, your vet can assess whether monitoring or supportive care is warranted.

Talk to your vet before starting CBD if your dog has pre-existing liver disease, kidney disease, or is on multiple medications. CBD has been studied primarily in healthy dogs or dogs with specific conditions like osteoarthritis, and safety in dogs with organ dysfunction is less well characterized.