Call ASPCA Poison Control: (888) 426-4435 or go to your nearest emergency vet. Do not wait for symptoms to appear.
Onions, garlic, leeks, and chives contain thiosulfate compounds that damage red blood cells, causing haemolytic anaemia. All forms are toxic — raw, cooked, dried, and powdered. Onion powder is especially dangerous because it is highly concentrated. Toxicity is cumulative, meaning repeated small exposures (e.g., leftover food with onion) can build up to a dangerous level over days.
Shih Tzus are brachycephalic — their flat facial structure restricts airflow and makes respiratory compromise from vomiting or toxic exposure more dangerous than in longer-nosed breeds. They are curious and bold for their size, often accessing food left unattended. Their kidney function can also be more sensitive than many breeds, making renal-toxic substances especially dangerous.
Why Does Breed Matter for Onions Toxicity?
Toxic doses for onions are calculated per kilogram of body weight. A Shih Tzu typically weighs 4–7.5 kg, which directly determines how much N-propyl disulfide (thiosulfate compounds) their body is exposed to relative to their size. Beyond weight, Shih Tzus have specific traits — outlined in the breed profile above — that can affect how quickly symptoms develop, how severe they become, and what complications to watch for.
When you call Poison Control, always give your dog's exact current weight, not a breed average. Even within the Shih Tzu breed, a significant weight difference changes the risk calculation meaningfully.
How Much Onions Is Toxic to a Shih Tzu?
These thresholds are based on the typical Shih Tzu weight range of 4–7.5 kg. Always use your dog's actual weight for the most accurate estimate. Use our Onion Toxicity calculator to enter your dog's exact weight.
| Dog weight | Mild signs | Serious signs | Potentially fatal |
|---|---|---|---|
| 4 kg (small Shih Tzu) | 20 g of raw onion | 40 g of raw onion | 120 g of raw onion |
| 5.5 kg (average Shih Tzu) | 28 g of raw onion | 55 g of raw onion | 165 g of raw onion |
| 7.5 kg (large Shih Tzu) | 38 g of raw onion | 75 g of raw onion | 225 g of raw onion |
ℹ️ Toxic dose is approximately 5g/kg of raw onion. Onion powder is ~5× more potent by weight. Cumulative exposure over multiple meals can cause anaemia without any single large ingestion. Source: ASPCA Animal Poison Control Center dose thresholds. Always confirm with your vet.
Symptoms of Onions Poisoning in Shih Tzus
Symptoms typically appear within Several days (haemolytic anaemia builds over time) of ingestion. Watch for:
Due to Shih Tzu-specific traits noted above, pay particular attention to any signs of breathing difficulty — their flat faces mean respiratory compromise can escalate rapidly compared to other breeds.
What to Do If Your Shih Tzu Ate Onions
- Stay calm and note how much they ate — estimate the amount and type of onions and your dog's weight. This information is critical for the vet.
- Call ASPCA Poison Control immediately — (888) 426-4435. Available 24/7. A $95 consultation fee may apply, but they will advise whether you need emergency care.
- Do not induce vomiting unless specifically instructed by a vet or Poison Control. Inducing vomiting incorrectly can cause additional harm.
- Go to an emergency vet if symptoms are already present, if a large amount was consumed, or if Poison Control advises it. Find a 24-hour emergency vet near you.
- Bring the packaging of the food or substance if possible — ingredient lists help the vet calculate exact toxin exposure.
Special Considerations for Shih Tzus
Like all brachycephalic breeds, Shih Tzus have increased aspiration risk during vomiting. Vets may use different decontamination protocols than they would for non-brachycephalic dogs. Their documented kidney sensitivity also means that renal-toxic substances (like grapes or certain NSAIDs) warrant aggressive fluid support and close monitoring of kidney values.
Frequently Asked Questions
No — cooking does not destroy the toxic thiosulfate compounds. Cooked, raw, dehydrated, and powdered onions are all toxic to dogs.
Approximately 5g of raw onion per kilogram of body weight is considered a toxic dose, but cumulative exposure from regular small amounts is also dangerous.
Yes — all Allium species (onions, garlic, leeks, chives, shallots) contain the same toxic compounds. Garlic is approximately 5× more potent than onion per gram.
Treatment involves decontamination if exposure was recent, followed by supportive care. Severe anaemia may require blood transfusion. N-acetylcysteine is sometimes used as a protective agent for red blood cells.