When you’re considering CBD oil for your dog, the first question usually isn’t “does it work?”
It’s “what could it do to my dog?”
That’s exactly the right question to ask. Understanding the side effects of CBD oil for dogs, and how well it’s tolerated, matters just as much as understanding the potential benefits. Any time you introduce a new prescription medication, knowing what to watch for is part of responsible care. (And while this guide focuses on dogs, we’ve included a note on cats too, since they respond a little differently.)
The reassuring news is that CBD in companion animals is now one of the more closely studied areas of veterinary cannabinoid research. Since 2018, controlled trials and long-term feeding studies have given us a much clearer picture of how dogs respond, what side effects to expect, and how those effects are managed in practice.
Here’s what the current evidence, as of 2026, actually shows.
How Well Is CBD Oil Tolerated in Dogs?
Across the veterinary literature, one theme comes up consistently: when appropriately dosed and prescribed, CBD is generally well tolerated in dogs.
Long-term feeding studies in healthy dogs have reported that daily CBD is well tolerated over extended periods, with side effects that are typically mild. A 36-week tolerability study also found that a lower daily dose was better tolerated than a higher one- a useful reminder that more is not better, and that dose matters.
This is reflected in real-world use, too. A large 2025 analysis from the Dog Aging Project reviewed data from more than 47,000 dogs and found CBD is most commonly given to older pets managing chronic issues such as arthritis, dementia and cancer- a reflection of how commonly CBD is now being used in older dogs managing chronic conditions, which makes understanding tolerability over time more important than ever.
Being well tolerated isn’t the same as being side-effect free, so it’s worth knowing what can actually happen.
What Are the Side Effects of CBD Oil for Dogs?
As with any medication, side effects are always possible.
In clinical trials of dogs taking CBD orally, the most commonly observed side effect has been mild, temporary diarrhoea or loose stools. Giving the oil with food can help reduce the likelihood of this happening. Across the research, gastrointestinal upset and vomiting tend to affect only a small percentage of dogs.
Less common side effects of CBD in dogs include:
- Mild sedation or drowsiness, usually at higher doses
- Reduced appetite or mild gastrointestinal upset
- Occasional changes such as redness around the ears
Dogs have generally been shown to tolerate CBD-predominant oil well, even at relatively high doses. Research has also consistently shown that CBD-predominant products are better tolerated than products containing higher concentrations of THC- one of the key reasons veterinary prescribing focuses on CBD rather than whole-plant products high in THC.
Can CBD Make My Dog Sleepy?
Mild drowsiness or sedation can occur, particularly when starting treatment or increasing the dose. This effect is typically dose-related and often improves as the pet adjusts or the dose is modified.
A Note on Cats
Cats metabolise CBD differently to dogs, so their side effect profile isn’t identical. The most frequently reported effects in cats are head shaking and increased licking. Some gastrointestinal effects have been linked to the carrier oil rather than the CBD itself, which is why carrier oil choice matters. You can read more in our guide to CBD for cats in Australia.
CBD and Liver Enzymes: What to Watch
One of the most discussed findings in CBD research is a modest elevation in liver enzymes (primarily ALP and ALT) sometimes seen in dogs taking CBD.
It’s worth putting this in context. While some studies have observed these increases, the clinical significance of these changes remains unclear, and other research suggests the changes may not be clinically significant. Even so, monitoring liver function during longer-term use is simply good clinical practice- and exactly the kind of thing a prescribing veterinarian keeps an eye on.
How CBD Side Effects Are Managed
Here’s the part that often gets lost online: most CBD side effects are mild, dose-related, and manageable under veterinary care. When CBD is prescribed and monitored properly, vets reduce the likelihood of side effects through a few well-established steps:
- Start low, go slow. Gradual dose titration helps find the lowest effective dose.
- Baseline and ongoing bloodwork. Liver enzyme monitoring keeps things stable over time.
- Reviewing other medications. CBD can interact with certain drugs, particularly some anti-epileptic medications.
- Giving CBD with food. A simple step that helps minimise gastrointestinal upset.
With this kind of structured approach, side effects can often be avoided altogether- or quickly resolved if they appear.
Why Product Quality Matters
This is one area where caution is non-negotiable. CBD products sold online most likely do not undergo the same quality control and regulatory oversight as veterinary-prescribed products, so there’s no guarantee of the actual CBD content, and no assurance the product is free from contaminants such as pesticides, solvents or heavy metals. Some may also contain unknown levels of THC- and dogs are far more sensitive to THC than humans.
In Australia, CBD is a scheduled substance and is only legal for pets when prescribed by a veterinarian. A prescription isn’t just a legal formality- it’s your assurance that the product is quality-controlled, appropriately dosed, and monitored by someone qualified to do so. For more on the rules, see our 2026 guide to whether CBD is legal for pets in Australia.
A Measured, Evidence-Based Approach
Understanding side effects isn’t about creating worry- it’s about supporting confident, informed care. CBD is not a cure, and it doesn’t replace conventional treatment. It’s best understood as one potential part of a broader management plan, alongside appropriate medication, nutrition, mobility support and regular veterinary assessment.
If you think CBD may help improve your dog’s quality of life, speak with your veterinarian about whether it’s appropriate, and what monitoring would look like.
If you don’t currently have a veterinarian experienced in cannabinoid prescribing, CBD Vets Australia can help connect you with qualified professionals. Reach out to us HERE to discover your local prescribing vet, or contact the CBD Vets Australia team HERE with any questions.
This article reflects peer-reviewed veterinary literature and Australian regulatory frameworks available as of 2026. Individual responses vary. Pet owners should consult a qualified veterinarian before introducing any new therapy.
