Black walnut
ToxicBlack walnut is toxic to dogs. Fallen nuts and hulls grow Penicillium that produces tremorgenic mycotoxins such as penitrem A, causing violent tremors and seizures within 30 minutes to 3 hours. Go to a vet immediately.
This food guide has not been reviewed by a veterinarian. It summarises general information from sources and should not be used to decide whether a food is suitable for an individual dog or to assess an emergency.
Check before feeding
Do not offer as a treat
There is no recommended treat portion for this hazardous item. If swallowed, contact a vet with the amount, time and product details. Do not induce vomiting yourself.
Signs and health concerns
This list includes both observable signs and conditions identified through examination or testing. It cannot establish the cause or whether an exposure is safe.
- Vomiting
- Muscle tremors
- Heightened sensitivity to touch or stimuli
- Poor coordination or balance
- Involuntary eye movements
- Fast heartbeat
- Overheating
- Seizures
More about this food
Black walnut (Juglans nigra) needs to be handled separately from the English walnut in your baking aisle. The danger is not the kernel's nutrition — it is the mould that thrives on the hull and on nuts that have been lying on the ground. In a documented canine intoxication, penitrem A produced by Penicillium crustosum was isolated from the mouldy walnuts the dog had eaten. Penitrem A blocks high-conductance calcium-activated potassium (BK) channels and impairs GABAergic transmission. With inhibition stripped out of the circuit, muscles fire uncontrollably. Roquefortine C, usually found alongside it, pushes in the same direction.
There is no safe dose. A small amount of mouldy hull material is enough to produce signs. Onset is typically 30 minutes to 3 hours: vomiting first, then muscle tremors and intention tremors that worsen when the dog tries to move deliberately, hyperesthesia (an exaggerated reaction to sound or touch), ataxia, nystagmus, tachycardia, hyperthermia driven by the tremoring itself, and seizures. Sustained high body temperature and continued convulsions can cause rhabdomyolysis and kidney injury, which is why this kills dogs that are otherwise healthy.
This matters in a specifically American way. Black walnut trees are common in yards and parks across the eastern and midwestern US, and dogs graze on the fallen green hulls through autumn. If your dog ate any, call your veterinarian now, or the ASPCA Animal Poison Control Center at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661. Do not induce vomiting at home — it is contraindicated in a tremoring or seizing animal and risks aspiration. Treatment is methocarbamol or a comparable muscle relaxant, sedation, active cooling, IV fluids, and intravenous lipid emulsion in severe cases. Signs can persist 24 to 72 hours, so expect hospitalisation.
The same syndrome comes from mouldy cheese, mouldy bread, spoiled pasta and compost piles. Rake the nuts, fence the compost.
Frequently asked questions
- My dog chewed a black walnut hull but spat it out. Is that fine?
- Not necessarily. Tremorgens act at very small doses and you cannot know how much was swallowed while chewing. The 30-minute to 3-hour window is when signs appear, so call your vet or poison control rather than simply watching.
- He is tremoring right now. What do I do before I get there?
- Treat it as an emergency and drive. Reduce stimulation — dim, quiet, minimal handling — and do not offer food, water or anything to induce vomiting. Note what was eaten and when, and bring a sample of the material if you can.
- Is black walnut dangerous to other animals too?
- Yes. Black walnut is separately toxic to horses through juglone, classically causing laminitis from black walnut shavings used as bedding. That is a different mechanism from the tremorgenic mycotoxicosis dogs get.