Onion / garlic (Allium cepa / Allium sativum)
Onion contains compounds that damage red blood cells and cause haemolytic anaemia with Heinz bodies. "Consumption of as little as 5 g/kg of onions in cats or 15 to 30 g/kg in dogs has resulted in clinically important hematologic changes." A relatively high single/short-term dose (600–800 g) can damage red blood cells. Onion is also toxic to cats; garlic is toxic to horses at >0.2 g/kg.
Grapes / raisins
Grape/raisin ingestion is linked to acute renal failure in dogs (idiosyncratic). "Estimated amounts of grapes associated with renal injury in dogs are about 32 g/kg; amounts of raisins associated with signs range from 11–30 g/kg." "The ingested doses involved in these fatal cases ranged from 10 to 57 g of fruit per kg b. wt."
Macadamia nuts
Macadamia contains an unknown toxin affecting muscles/神经系统 in dogs. "The toxic dose to dogs ranges from 2.4–62.4 g per kg b.wt." — a very wide range, so some dogs react at low doses.
Xylitol (mechanism, no established threshold in this source)
"Xylitol, an artificial sweetener, is present in many products, such as candy, sugar-free chewing gums, toothpaste and baked goods." Unlike humans, "in dogs, xylitol is a strong promoter of insulin release, which results in a rapid decrease in blood glucose (hypoglycemia)," causing an insulin-mediated hypoglycemic crisis (Cope 2004; Dunayer 2004). This source documents the mechanism but states no single mg/kg threshold.
Source: pdf-raw/pmc-pet-food-toxic-pmc2984110.txt — first-hand peer-reviewed review "Some food toxic for pets" (PMC2984110, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2984110/), Tavily server-side extract 2026-07-21.