Written by 
Theobromine (say “thee-oh-BROH-meen”): a natural stimulant found in cocoa. Together with caffeine, it is the substance that makes chocolate poisonous to dogs and cats.
If your pet has just eaten chocolate, go straight to My dog ate chocolate: what to do right now, or call your vet or a poison line: ASPCA Animal Poison Control at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661. Both may charge a fee.
What it is
Chocolate is made from the roasted seeds of the cacao tree, Theobroma cacao. Those seeds contain two closely related stimulants, theobromine and caffeine. Chemists group them as methylxanthines. According to the Merck Veterinary Manual, chocolate holds 3 to 10 times as much theobromine as caffeine, and both add to the poisoning.
What it does in the body
Theobromine blocks receptors for adenosine, a natural chemical that calms cells down. With that brake off, the nervous system and the heart are overstimulated. The result is restlessness, a fast heart rate and more urine. It also raises calcium levels inside muscle cells, which makes the heart and body muscles contract harder. At high doses this leads to tremors, seizures and dangerous heart rhythms.
Why dogs are so sensitive
The difference is speed. People clear theobromine fairly quickly. Dogs do not. The Merck Veterinary Manual gives theobromine a half-life of about 17.5 hours in dogs, compared with about 4.5 hours for caffeine. A half-life is the time the body takes to remove half of a substance, so a large amount lingers for days.
Two more things keep it in the body. After the liver processes it, some passes back into the gut and is absorbed again. It can also be reabsorbed from urine sitting in the bladder, which is why vets encourage a poisoned dog to urinate often.
Many species can be poisoned by theobromine. Dogs are affected most often because they eat almost anything they can reach.
How much is in chocolate
The more cocoa, the more theobromine. This table shows the combined theobromine and caffeine content of common products.
| Product | Methylxanthines per ounce |
|---|---|
| Cocoa powder | 807 mg |
| Unsweetened (baking) chocolate | 440 mg |
| Cocoa bean hulls (garden mulch) | 255 mg |
| Semisweet and sweet dark chocolate | 150 to 160 mg |
| Milk chocolate | 64 mg |
| White chocolate | 1.1 mg |
Source: Merck Veterinary Manual, Chocolate Toxicosis in Animals (viewed November 2026). Amounts vary with the bean and the brand, and some cocoa mulch has had the stimulants removed.
How much is dangerous
The US Food and Drug Administration says mild signs are possible from about 9 mg of theobromine per pound of a dog’s body weight, and severe signs from around 18 mg per pound. Its example: 6 ounces of semisweet chips holds about 816 mg. For a 60-pound dog that works out to about 13.6 mg per pound, likely mild to moderate signs. For a 6-pound dog it is about 136 mg per pound, which can kill without treatment.
Individual dogs vary in how sensitive they are. Do not use these figures to decide to wait. Use them to see why a small dog and dark chocolate are a bad mix, then call.
Signs of theobromine poisoning
Cornell’s Riney Canine Health Center says signs may appear 2 to 12 hours after eating chocolate and can last 12 to 36 hours, or longer in severe cases.
- Early: vomiting, diarrhea, heavy thirst, a bloated belly, restlessness.
- Worsening: hyperactivity, a lot of urination, panting, a racing or irregular heartbeat, wobbliness, tremors.
- Severe, go now: seizures, a very high temperature, collapse or coma.
A dog with severe signs needs a 24-hour emergency vet at once.
What the vet does
Treatment aims to get theobromine out and control its effects until the body clears it. If the chocolate was eaten recently, the vet may give a medicine to make your dog vomit, and sometimes activated charcoal to bind what is left in the gut. Dogs with signs are usually admitted for fluids into a vein, heart monitoring, and medicines for vomiting, tremors, seizures or abnormal heart rhythms.
The bill depends on how long your dog stays and what monitoring is needed. Our guide to what a vet visit costs explains exam fees and common add-ons.
Do not try to make your dog vomit at home unless a vet or poison line tells you to and explains how.
Cats
Theobromine is toxic to cats too, with the same kind of signs. Cats cannot taste sweetness, but that does not protect them, and darker chocolate is more dangerous for them as well. Treat it the same way: call your vet or a poison line.