According to the ASPCA, thousands of dogs needlessly suffer (and many die) each year by ingesting these common household foods and substances. If you suspect that your pet has eaten any of them, seek emergency help right away.
Alcoholic beverages. Because alcohol can be fatal to dogs, no amount of alcoholic beverage is safe- yes; even beer should be off limits.
Chocolate is toxic to canines. The darker the chocolate, the more harmful. The methylxanthines (caffeine and theobromine) in chocolate can cause a dog to vomit, have diarrhea, experience rapid, irregular heart beat, have increased urination, and experience muscle tremors and seizures. The effects can be serious. Death from chocolate toxicity can occur with 24 hours.
Coffee, tea and cola are people-food. They contain caffeine, a methylxanthine also found in chocolate. The signs of toxicity include rapid heart beat, hyperexcitability, tremors, and seizures.
Macadamia nuts can temporarily cause muscle weakness, often in the hind legs. Other signs include vomiting, fever, and abdominal pain. The mechanism of the toxicity is unknown. Affected dogs recover with no treatment and no long-term effects.
Onions and garlic have a chemical that damages red blood cells in dogs and can cause anemia. Even one small whole onion can cause death. So be particularly careful when disposing of left-overs that contain a significant amount of onions, such as pizza or Chinese take-out. The small amounts of onion and garlic powder used in pet foods is safe and well below the toxic levels.