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Are Walnuts Toxic to Dogs? Black vs English Walnuts Explained

PawAI Lab
7 min read

Learn which types of walnuts may pose a risk to dogs, why moldy walnuts are a particular concern, and what steps to take if your dog has eaten walnuts.

Quick Answer

Walnuts can be harmful to dogs, and the level of risk depends on the type. Black walnuts contain juglone, a compound that may cause illness in dogs. English walnuts are not inherently toxic, but their high fat content can lead to gastrointestinal upset or pancreatitis. Walnuts that have become moldy may contain tremorgenic mycotoxins, which can cause tremors or seizures. If your dog ate walnuts, contact a veterinarian or an animal poison-control service for guidance.

Before using any tool, contact a veterinary professional if your dog may have eaten walnuts, especially if they were moldy or black walnuts.

  • US: ASPCA Animal Poison Control (888-426-4435) or Pet Poison Helpline (855-764-7661)
  • UK: Animal PoisonLine (01202 509000) or your nearest veterinary emergency clinic
  • Canada: ASPCA Animal Poison Control (888-426-4435) or Pet Poison Helpline (855-764-7661)
  • AU: Animal Emergency Centre or your regular vet
  • EU: Contact your nearest veterinary emergency service

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Safety Verdict

Potentially Harmful. The risk from walnuts varies with the type and condition of the nut. Three main concerns apply to dogs:

  • Black walnuts contain juglone, a naturally occurring compound that is associated with gastrointestinal and neurological signs in dogs. Black walnut trees and their fallen hulls are the usual source of exposure.
  • English (common) walnuts are not considered directly toxic, but they are high in fat. Large amounts can cause vomiting, diarrhea, or inflammation of the pancreas (pancreatitis), which can be serious.
  • Moldy walnuts of any type may contain tremorgenic mycotoxins, such as penitrem A and roquefortine. These substances are produced by certain molds and can cause muscle tremors, seizures, and other neurological signs in dogs.

Because mold contamination is not always visible, any walnut that has been on the ground for an extended period should be treated with caution.

What Should the Owner Do Now?

  1. Contact a veterinarian or animal poison-control service. This is especially important if your dog ate black walnuts, moldy walnuts, or a large quantity of English walnuts.
  2. Determine the type of walnut. If possible, identify whether the walnuts were black or English, and whether they were in the shell, shelled, or part of a baked good.
  3. Check for signs of mold. Moldy walnuts may appear fuzzy, discolored, or shriveled, but mold is not always visible. Note any damp or musty smell.
  4. Do not induce vomiting unless a veterinarian or poison-control professional directly instructs you to do so.
  5. Do not give food, milk, salt, charcoal, or any home remedy. These are not proven treatments and may worsen the situation.
  6. Follow the veterinarian's instructions regarding whether to bring your dog in for examination or monitoring.

What Signs May Occur?

Signs may develop within hours of ingestion, though the timeline can vary depending on the type of walnut and whether mold toxins are involved. Not all signs appear in every dog, and the absence of early symptoms does not rule out risk.

Signs associated with gastrointestinal irritation or high fat intake may include:

  • Vomiting
  • Diarrhea
  • Reduced appetite
  • Abdominal pain or discomfort

Signs that may suggest pancreatitis include:

  • Repeated vomiting
  • Hunched posture or abdominal pain
  • Lethargy or weakness

Signs that may suggest tremorgenic mycotoxin exposure from moldy walnuts include:

  • Muscle tremors or shaking
  • Unsteadiness or lack of coordination
  • Seizures
  • Rapid breathing or elevated body temperature

Moldy walnut exposure can progress quickly, so tremors or seizures should be treated as an emergency.

What Information Should Be Ready?

When you contact a veterinarian or poison-control service, having the following details available can help them assess the situation more efficiently:

  • Dog's details: species, breed, approximate age, and body weight
  • Type of walnut: black walnut, English walnut, or unknown; in the shell or shelled; part of a food product (e.g., banana bread, cookies)
  • Condition of the walnut: whether it was fresh, old, moldy, or found on the ground
  • Estimated amount: best guess of how many walnuts or how much of a food product was eaten
  • Time of ingestion: when the exposure occurred, or the window of time during which it may have happened
  • Current symptoms: any vomiting, diarrhea, tremors, weakness, or changes in behavior
  • Packaging: if available, the ingredient list from any prepared food involved
  • Medical history: any pre-existing pancreatitis, gastrointestinal conditions, current medications, or other health conditions

Differences That May Affect Risk

Walnut-related risk in dogs is influenced by several factors:

  • Type of walnut: Black walnuts pose a different risk profile than English walnuts because of juglone content.
  • Mold contamination: Tremorgenic mycotoxins can be present even when mold is not clearly visible. Walnuts left outdoors or stored improperly carry greater concern.
  • Body size: Smaller dogs may be more affected by a given amount of walnut or fat.
  • Fat sensitivity: Dogs with a history of pancreatitis or sensitive digestion may react more strongly to the high fat content of walnuts.
  • Pre-existing conditions: Dogs with neurological, gastrointestinal, or pancreatic conditions may be more vulnerable.

Because of these variables, any ingestion of walnuts should be discussed with a veterinarian, especially if mold or black walnuts are involved.

When to Contact a Veterinarian

Contact a veterinarian or animal poison-control service promptly if your dog has eaten walnuts, particularly black walnuts or walnuts that may have been moldy.

Emergency signs that require urgent veterinary attention include:

  • Muscle tremors, shaking, or seizures
  • Unsteadiness or loss of coordination
  • Repeated or persistent vomiting
  • Severe diarrhea
  • Lethargy, weakness, or collapse
  • Signs of abdominal pain

Non-urgent follow-up: If your dog ate a small number of fresh English walnuts and appears normal, a veterinary consultation is still recommended to confirm whether monitoring at home is appropriate or whether an examination is advisable.

FAQ

Can dogs eat English walnuts?

English walnuts are not considered directly toxic to dogs, but they are high in fat and can cause gastrointestinal upset or pancreatitis. They are not a recommended treat, and larger amounts or frequent feeding increase the risk of complications.

Are black walnuts toxic to dogs?

Black walnuts contain juglone, a compound associated with illness in dogs. Fallen black walnuts with their hulls attached, or walnuts that have begun to decompose, are of particular concern. A veterinarian can assess the specific situation after known or suspected exposure.

What happens if a dog eats moldy walnuts?

Moldy walnuts may contain tremorgenic mycotoxins that can cause muscle tremors, unsteadiness, and seizures in dogs. This is considered an emergency. If your dog ate walnuts that may have been moldy, contact a veterinarian or animal poison-control service immediately.

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Disclaimer

This article and the PawAI Toxicity Checker provide general safety information and cannot determine an individual pet's toxicity risk or replace a veterinarian or animal poison-control service. If exposure may have occurred, contact an appropriate professional promptly, even if your pet appears well.

Written by PawAI Lab