Is Walnuts Toxic to Cats and Dogs?
Walnuts are moderately toxic to dogs, mainly when moldy — fallen black walnuts can cause tremors and seizures. Cats are mildly affected. Call a vet if moldy nuts are eaten.
Can cause real harm — call a vet for guidance.
Usually minor, but watch for symptoms.
In an emergency, do not wait.
Medical disclaimer: This tool is for general information only and isnot a substitute for veterinary diagnosis or treatment. Toxicity depends on the amount, your pet’s size, and health history. If your pet may have ingested something harmful, contact your veterinarian or a poison control hotline ((888) 426-4435 / (855) 764-7661) immediately — do not wait for symptoms to appear.
What is Walnuts?
Walnuts are moderately toxic to dogs, mainly when moldy — fallen black walnuts can cause tremors and seizures. Cats are mildly affected. Call a vet if moldy nuts are eaten.
Also known as: black walnut, english walnut, moldy walnuts, walnut shell.
Symptoms to Watch For
🐕 In Dogs
- Vomiting and diarrhea
- Tremors or seizures from moldy walnuts (tremorgenic mycotoxins)
- Abdominal pain and reduced appetite
- Blockage risk from shells
🐈 In Cats
- Vomiting and diarrhea
- Reduced appetite
What to Do If Ingested
- Remove any remaining walnuts.
- Note whether they were moldy (fallen/black walnuts are riskiest).
- Call a veterinarian or poison hotline.
Steps apply to both cats and dogs. When in doubt, call a vet or poison hotline before acting.
When to Call the Vet Immediately
Call your veterinarian or a poison control hotline right away if you notice any of these:
- Moldy or fallen black walnuts were eaten
- Tremors, seizures, or vomiting
- A shell was swallowed
Frequently Asked Questions
Frequently Asked Questions
Why are fallen or moldy walnuts dangerous?
Walnuts that fall and sit on the ground can grow mold that produces tremorgenic mycotoxins, which cause tremors and seizures in dogs. Black walnuts are especially associated with this risk. Store-bought fresh walnuts are lower risk but can still cause stomach upset.
Can walnut shells cause problems?
Yes. Walnut shells are hard and indigestible, so swallowing them can cause choking or intestinal blockage. Keep shells and whole nuts out of reach.
What are the signs of moldy walnut poisoning?
Vomiting, muscle tremors, and seizures can develop within hours of eating moldy walnuts. This can progress quickly, so call a vet immediately if tremors appear.
Sources
This entry is reviewed against the following authoritative veterinary sources.
Last reviewed: 2026-07-11