Why walnuts are toxic to dogs
Per Munday 2017 (New Zealand Vet J) review of tremorgenic mycotoxicosis in companion animals, Boysen 2002 (J Vet Emerg Crit Care) case series of penitrem-A toxicosis in dogs, and Hovda 2014 (Vet Clin North Am) on tremorgenic mold ingestion, walnuts are toxic to dogs primarily because they are highly susceptible to fungal colonization — particularly with Penicillium species producing penitrem A and roquefortine C. These tremorgenic mycotoxins act on the central nervous system as GABA antagonists producing the classic tremorgen-toxicosis triad: fine muscle tremors, ataxia, and hyperthermia progressing to seizures if untreated. Penitrem-A LD50 in dogs is approximately 0.5 mg/kg per Munday 2017 — meaning a 20 lb dog can show clinical signs after eating a handful of moldy walnuts.
Walnuts harvested in fall and left on the ground (common in yards with walnut trees, particularly black walnut) are particularly high-risk because of accumulated mold colonization over weeks of ground contact. Old walnuts in pantries can also harbor mold even without visible discoloration — the mold colonies grow inside the nutmeat before showing visible signs. Black walnut hulls (Juglans nigra) contain juglone, a quinone allelopathic toxin per Hovin 1972 (Bot Gaz) primarily affecting horses (juglone-bedding-induced laminitis is the classic veterinary syndrome) but also implicated in some canine GI signs after black-walnut hull contact or ingestion. English walnuts (Juglans regia) contain much less juglone but are still mold-susceptible. Walnut high fat content (~65% fat by weight, predominantly polyunsaturated) triggers pancreatitis in susceptible breeds (miniature schnauzers, Yorkshire terriers, hyperlipidemic dogs per Watson 2008) at modest ingestion quantities.
How many walnuts are dangerous for a dog
Per Munday 2017 (New Zealand Vet J), even a handful of moldy walnuts can produce tremorgenic mycotoxicosis in a small or medium dog. Penitrem-A LD50 in dogs is approximately 0.5 mg/kg body weight; mycotoxin content of contaminated walnuts is variable but can reach 0.1–1 mg penitrem-A per gram of moldy nutmeat. Practical dose calculations for moldy walnuts: a 20 lb (9 kg) dog can reach clinical-signs threshold from ~5–10 g of contaminated walnut (equivalent to 2–4 nutmeats). A 50 lb (23 kg) dog reaches threshold from 15–25 g (6–10 nutmeats). Fresh non-moldy walnuts in small amounts (1–2 nutmeats) for a large dog may produce only mild GI upset, but any moldy walnut is an emergency regardless of dog size. Whole walnuts in the shell add GI obstruction risk per Hayward 2002.
Walnut-containing foods to avoid sharing: walnut bread, walnut brownies, walnut-encrusted desserts, banana bread with walnuts, walnut pesto, walnut oil dressings (high fat load), walnut butter, candied walnuts, glazed walnuts (high sugar), Waldorf salad, and any baked goods with walnuts (often also contain xylitol, chocolate, or raisins which compound the toxicity). Yard exposure is a major risk for residential properties with walnut trees: black walnut trees drop nuts in fall that remain on the ground for weeks accumulating mold; English walnut trees produce similar fall windfalls. Fence off the drop zone or pick up walnuts daily during fall harvest. Hickory nuts and pecans are similar (same Juglandaceae family) and carry comparable risks — see the related can-dogs-eat-pecans page. Macadamia nuts have a different toxicity mechanism (tremorgenic of unknown specific cause) but similar emergency status — see can-dogs-eat-macadamia-nuts.
Symptoms of walnut poisoning in dogs
Per Munday 2017 (New Zealand Vet J) and Boysen 2002 (J Vet Emerg Crit Care), tremorgenic mycotoxicosis from moldy walnuts presents within 1–3 hours of ingestion with characteristic signs: fine muscle tremors (often the first sign — fasciculations starting in face / shoulders / hindquarters), generalized whole-body tremors progressing rapidly within hours, ataxia (uncoordinated movement) and difficulty standing, hyperthermia (body temperature greater than 105 F / 40.5 C due to sustained muscle activity), tachycardia and tachypnea, hyperesthesia (exaggerated startle response to touch / sound), vomiting (sometimes early sign), seizures (most concerning sign — can progress to status epilepticus without treatment), opisthotonos (rigid arching of head and neck backward) in severe cases, and death from hyperthermia, seizures, or aspiration without treatment. Pancreatitis from high-fat walnut ingestion presents over 12–48 hours with persistent vomiting, abdominal pain, anorexia, and lethargy. Both presentations require emergency veterinary care.
What to do if your dog ate walnuts
Treat any moldy-walnut ingestion or suspected walnut ingestion with tremor signs as a category-1 emergency. (1) Call ASPCA Animal Poison Control at 1-888-426-4435 or Pet Poison Helpline at 1-855-764-7661 for case-management guidance. (2) Do not wait for full symptom development — tremorgens act quickly and treatment is most effective when started early. (3) Do not induce vomiting at home if your dog is showing tremors or has any neurologic signs (high aspiration risk). For early-presentation cases without signs, induced emesis may be appropriate per APCC guidance. (4) Transport immediately to nearest 24-hour emergency veterinary hospital. (5) Bring information: estimated quantity ingested, source (yard tree vs pantry vs baked goods), whether walnuts appeared moldy or old, dog's weight, time of ingestion, and current symptoms.
Hospital treatment for tremorgenic mycotoxicosis per Munday 2017 and Boysen 2002: induced emesis if recent (within 2 hours) and no neurologic signs yet, activated charcoal with sorbitol (repeated dosing because mycotoxins undergo enterohepatic recirculation), methocarbamol (Robaxin) IV as the primary muscle relaxant of choice for tremorgen toxicosis — titrated to effect, diazepam or midazolam for seizure control, active cooling for hyperthermia (cool IV fluids, fans, isopropyl alcohol on paw pads), IV fluid therapy for tachycardia + tachypnea + electrolyte support, continuous neurologic monitoring, and respiratory support if needed. Most cases recover within 24–72 hours with aggressive treatment; severe cases with status epilepticus or sustained hyperthermia have guarded prognosis. For walnut-pancreatitis: NPO + IV fluids + antiemetics + analgesia + monitoring over 3–7 days. Prevention: secure or pick up windfall walnuts during fall harvest; discard old pantry walnuts at any sign of mold or rancidity; never share walnut-containing baked goods; brief house guests not to share trail mix / walnut snacks.
Frequently asked questions
Are walnuts toxic to dogs?
Yes — walnuts are toxic to dogs via three mechanisms. (1) Tremorgenic mycotoxin syndrome from moldy walnuts containing penitrem A and roquefortine C produced by Penicillium molds per Munday NZ Vet J 2017 and Boysen JVECC 2002. Symptoms (tremors, ataxia, hyperthermia, seizures) appear within 1-3 hours; penitrem-A LD50 in dogs is approximately 0.5 mg/kg. (2) Juglone toxin from black walnut hulls per Hovin 1972 — primarily equine concern but also implicated in canine GI signs. (3) High fat content (~65% by weight) triggers pancreatitis in susceptible breeds (miniature schnauzers, Yorkies, hyperlipidemic dogs per Watson JSAP 2008). Black walnuts are higher-risk than English walnuts. Treat any walnut ingestion as a category-1 emergency.
What if my dog ate just a few walnuts?
Even a handful of moldy walnuts can produce tremorgenic mycotoxicosis in a small or medium dog. Penitrem-A LD50 is approximately 0.5 mg/kg per Munday 2017; mycotoxin content of contaminated walnuts can reach 0.1-1 mg per gram of moldy nutmeat. A 20 lb dog can reach clinical-signs threshold from ~5-10 g of contaminated walnut (2-4 nutmeats). Fresh non-moldy walnuts in small amounts may produce only mild GI upset in a large dog, but you cannot reliably tell whether a walnut is moldy without lab testing — mold colonies often grow inside the nutmeat before showing visible signs. Pantry walnuts that are even slightly old or yard walnuts that were on the ground are higher risk. Treat any walnut ingestion as concerning and call ASPCA Animal Poison Control (1-888-426-4435).
What are the symptoms of walnut poisoning in dogs?
Per Munday 2017 and Boysen 2002, tremorgenic mycotoxicosis from moldy walnuts presents within 1-3 hours of ingestion with characteristic signs: fine muscle tremors (often the first sign — fasciculations starting in face / shoulders / hindquarters), generalized whole-body tremors progressing rapidly, ataxia and difficulty standing, hyperthermia (body temperature greater than 105 F due to sustained muscle activity), tachycardia and tachypnea, hyperesthesia (exaggerated startle response), vomiting, seizures (can progress to status epilepticus), opisthotonos (rigid arching of head and neck backward) in severe cases, and death from hyperthermia / seizures / aspiration without treatment. Pancreatitis from high-fat walnut ingestion presents over 12-48 hours with persistent vomiting, abdominal pain, anorexia, and lethargy. Both presentations require emergency veterinary care.
For related context, see our Can Dogs Eat Macadamia Nuts? and Can Dogs Eat Pecans?. To check whether your dog’s food contains any of these ingredients, paste the ingredient list into the KibbleIQ analyzer. For methodology context, see our published methodology.