Theobromine: Why Chocolate Poisons Dogs, in Milligrams per Kilogram

A dog eats half a bar of dark chocolate while you answer the door, and suddenly you are doing arithmetic with your heart rate. The question is never "is chocolate bad for dogs" — it is "how bad is this much chocolate, for this dog, right now". That question has a real answer, and it is expressed in milligrams per kilogram.

What theobromine is, and why dogs cannot clear it

Theobromine is the bitter alkaloid in cacao — a cousin of caffeine that gives dark chocolate its edge. Humans metabolise it in a few hours. Dogs clear it roughly six times more slowly, so it lingers: heart rate climbs, the nervous system stirs, and what a person would shrug off becomes, in a 10 kg dog, a medical event. Cats are sensitive too but almost never eat chocolate, because they cannot taste sweetness — practically every real case involves a dog. The caffeine in chocolate adds a little extra stimulation, but theobromine is the payload.

The reference table: not all chocolate is equal

Theobromine content tracks how much actual cacao is in the food, and the published reference values span two orders of magnitude. Cocoa powder runs about 26 mg per gram; unsweetened baking chocolate about 14 mg/g; dark and semi-sweet eating chocolate about 5.5 mg/g; milk chocolate about 2 mg/g; white chocolate a negligible 0.25 mg/g. Those numbers are why the same 100 g incident is a shrug in milk form and an emergency in baking form: 200 mg of theobromine versus 1,400. Values vary by brand and cocoa percentage, so treat them as midpoints of published ranges — the Chocolate Toxicity Calculator uses exactly this table.

Dose bands: what the mg/kg numbers mean

Divide total theobromine by the pet's body weight and you get the dose that vets actually reason with. The commonly used thresholds: below about 15 mg/kg, most pets show nothing worse than possible stomach upset; from 15 to 39 mg/kg, vomiting, diarrhea and restlessness become likely and vets usually want the call within the first hour or two; from 40 to 59 mg/kg, heart-rhythm disturbances and tremors enter the picture; at 60 mg/kg and above, seizures become possible and the case is potentially life-threatening. Lethal doses cluster far higher — but "probably survives" is not the bar any owner wants, which is why every band above the first is a phone call, not an observation.

The arithmetic of one incident

Work an example through. A 20 kg Labrador eats 100 g of dark chocolate: 100 × 5.5 = 550 mg of theobromine, divided by 20 kg gives 27.5 mg/kg — the moderate band, an urgent call. The same 100 g eaten by a 4 kg terrier is 137.5 mg/kg, deep in life-threatening territory. Flip it around and the numbers explain themselves: for that Labrador, milk chocolate stays under 15 mg/kg until roughly 150 g, while for the terrier the same boundary is at 30 g — a single row of a chocolate bar. Weight is the denominator of the whole calculation, which is why small dogs land in emergency rooms over amounts that would barely register for a big one.

What to do, and what not to do

Call first: your veterinarian, or a pet poison line — in the US, ASPCA Animal Poison Control (888-426-4435) or Pet Poison Helpline (855-764-7661). Have the chocolate type, the estimated amount and the pet's weight ready; that is the same arithmetic this calculator performs. If a vet advises making the pet vomit, the first one to two hours matter enormously, before the theobromine is fully absorbed. Do not wait for symptoms — by the time tremors or a racing heart appear, the toxin is already working. And do not rely on home remedies: salt, hydrogen peroxide dosing and "making them drink milk" all add risk. Treat the calculator as a screening tool that informs the call, never as a verdict that no call is needed — only a professional who can see the animal can make treatment decisions.

Try it yourself

Open the Chocolate Toxicity Calculator and run the numbers for your own pet's weight before you ever need them — the calm moment is the right time to learn that a 100 g milk-chocolate incident is moderate for your 25 kg dog but life-threatening for the neighbour's 5 kg one. Try each chocolate type at the same amount to feel the two-orders-of-magnitude spread, and check the "to reach the moderate band" row, which shows the gram threshold for your specific pet. The age curves behind your pet's life stage live in how dog years work and how cat years work, and the yearly budget that keeps a chocolate-fiend fed lives in the Pet Annual Cost Calculator.