Why chocolate is toxic to dogs
Chocolate contains theobromine and caffeine (together: methylxanthines), stimulants that humans metabolize quickly but dogs clear very slowly — theobromine's half-life in dogs is about 17.5 hours (Merck Veterinary Manual). The stimulant builds up, overstimulating the heart and nervous system. The darker the chocolate, the more theobromine per ounce, which is why a few squares of baking chocolate can be an emergency while the same amount of milk chocolate may only mean an upset stomach.
Methylxanthine content by chocolate type
| Chocolate type | Methylxanthines (Merck Vet Manual) |
|---|---|
| White chocolate | ~1 mg/oz |
| Milk chocolate | ~64 mg/oz |
| Dark / semi-sweet | 150–160 mg/oz |
| Baking chocolate (unsweetened) | ~440 mg/oz |
| Dry cocoa powder | ~807 mg/oz |
Symptom thresholds vets use
- ≥ 20 mg/kg — vomiting, diarrhea, restlessness, excessive thirst
- ≥ 40 mg/kg — cardiac signs: racing heart, arrhythmias, high blood pressure
- ≥ 60 mg/kg — neurological signs: tremors, twitching, seizures
- ≥ ~100–200 mg/kg — potentially fatal without treatment
Signs typically appear within 6–12 hours of ingestion. Because theobromine clears slowly, dogs can remain symptomatic for up to three days in serious cases.
Frequently asked questions
My dog ate chocolate — what should I do first?
Work out roughly how much and what type of chocolate was eaten, then use this calculator for the risk level. If the dose is moderate or higher, or you're unsure of the amount, call your vet or the Pet Poison Helpline (855-764-7661, US) immediately. Do not induce vomiting unless a professional tells you to.
How much chocolate is toxic to a dog?
Toxicity depends on the methylxanthine (theobromine + caffeine) dose per kg of body weight. Mild signs can start around 20 mg/kg, heart effects around 40-50 mg/kg, and seizures over 60 mg/kg (Merck Veterinary Manual). Dark and baking chocolate contain many times more methylxanthines than milk chocolate, so small amounts of dark chocolate are far more dangerous.
Is white chocolate dangerous for dogs?
White chocolate contains almost no methylxanthines (about 1 mg per ounce, per the Merck Veterinary Manual), so true chocolate poisoning is virtually impossible. The fat and sugar can still cause stomach upset or pancreatitis in large amounts.
How long after eating chocolate do symptoms appear?
Signs usually appear within 6 to 12 hours: restlessness, vomiting, diarrhea, panting, racing heart, tremors. Theobromine is slow to clear — symptoms can persist up to 72 hours in severe cases.