Herb and supplement-drug interactions in animals
Herbs and supplements can dangerously affect medicines in animals. Read about CBD interactions, liver risks and what to do in case of poisoning.
Short & honest
Moderate evidence (grade B) shows that herbs and supplements—including CBD—can disrupt the hepatic breakdown of medicines in animals, with potentially dangerous consequences.
Safety assessment: Caution — conditions and risks
Veterinary review not yet completed
This page is awaiting review by a registered veterinary surgeon. Until then, treat the text as education based on the sources listed — not as a verified veterinary judgement.
Why 'natural' does not equal safe
Herbs and supplements contain pharmacologically active substances. These substances can strengthen, weaken or disrupt the breakdown of conventional medicines in the liver. The veterinary literature on this subject is limited; the best documented example is cannabidiol (CBD) in dogs and cats.
Interactions via the liver enzyme system (CYP450)
Most medicines are broken down in the liver by enzymes of the cytochrome P450 family (CYP450). CBD inhibits multiple CYP450 enzymes [1][4], which can cause two types of problems:
- Accumulated drug levels: the medicine is broken down more slowly, causing the blood level to rise and overdose to occur.
- Reduced efficacy of prodrugs: medicines that are only converted to their active form in the liver work less effectively.
Documented risk combinations:
- CBD + phenobarbital (anti-epileptic): increased risk of hepatotoxicity [2][4]
- CBD + NSAIDs (anti-inflammatories): possible pharmacokinetic interaction [1]
- CBD + immunosuppressants or antibiotics: interactions via the same CYP450 pathways are possible [1]
Species-specific vulnerability
| Species | Point of attention |
|---|---|
| Dogs | Most studied species; increased liver values (ALT) demonstrated with higher and prolonged CBD administration [2][3] |
| Cats | Reduced capacity for certain metabolic pathways; greater toxicity risk with many compounds [4] |
| Other species | Hardly any controlled data available |
Increased liver values as an early signal
In several studies, liver enzymes (ALT) increased in healthy dogs receiving long-term CBD, even without visible symptoms [2][3]. This early biological signal indicates liver stress. When used concurrently with other hepatotoxic agents — such as phenobarbital — the threshold for damage is lower [4].
If toxicity is suspected
Stop the supplement immediately and call your veterinary surgeon or the veterinary emergency service. Preferably bring the packaging. Do not wait for symptoms to appear: hepatotoxicity can be present without immediate clinical signs [3][4].
Always share the complete medication list
Inform your veterinary surgeon always and fully about all supplements, herbs and foodstuffs your animal uses — even if they are available over the counter. This includes:
- Herbal mixtures and phytotherapeutic preparations
- CBD oil and other cannabinoids
- High-dose fatty acid supplements (omega-3/6)
- Mushroom extracts and adaptogens
Only with the complete overview can the veterinary surgeon safely align medication choices and dosages.
Why this verdict?
The grade B classification is based on several narrative reviews and safety studies on CBD in dogs [1][2][3][4]. The literature is methodologically limited: controlled intervention studies across multiple animal species and other supplement categories are largely absent, and transferability to other herbs or species is uncertain.
Interactions with medication
- CBD + phenobarbital: increased risk of hepatotoxicity due to CYP450 inhibition [2][4]
- CBD + NSAIDs: possible increase in drug levels via reduced hepatic breakdown [1]
- CBD + immunosuppressants or antibiotics: interactions via CYP450 pathways have been described [1]
Legal status (Netherlands)
In the Netherlands, treatment advice, medication choice and the use of supplements in sick animals fall under the Wet dieren (Animals Act) and are reserved for veterinary surgeons. This page is for informational purposes only.
Sources
- [1] Pharmacokinetics, efficacy, and safety of cannabidiol in dogs: an update of current knowledge. Frontiers in Veterinary Science, 2023. Narrative review doi:10.3389/fvets.2023.1204526
- [2] Long-term daily feeding of cannabidiol is well-tolerated by healthy dogs. Frontiers in Veterinary Science, 2022. Narrative review doi:10.3389/fvets.2022.977457
- [3] Safety study of cannabidiol products in healthy dogs. Frontiers in Veterinary Science, 2024. Narrative review source ↗
- [4] Toxicosis in Dogs and Cats From Cannabidiol (CBD). Merck Veterinary Manual, 2023. Monograph source ↗