A chemical reaction takes place inside the cat. Chocolate contains a chemical called theobromine which is toxic to cats and dogs. Unlike in humans, theobromine is not metabolised (broken down) by cats or dogs. This leads to a toxic build-up of the chemical. This then leads to problems with the cat’s heart, bowels, nervous system and kidneys. The last step in the chain reaction is that the cat can have seizures, heart failure. Possible death may occur in the most severe cases.
Fortunately, cats are not attracted to eating chocolate. So, a person would have to force it on a cat. That would be cat abuse and probably a crime under animal welfare laws. A killing dose is approximately 100 to 200 milligrams per kilogram of body weight. Toxicity symptoms occur at much lower doses. For cats and dogs, it is 20 milligrams per kg of body weight. Dogs are attracted to chocolate as they like sweet foods. Therefore, it is a real danger to dogs.
IMPORTANT: I am concerned that cat haters may concoct the idea that they want to kill a cat with chocolate. Don’t. It’d be a crime and if you were caught the punishment in developed countries is not insubstantial. Plus, you’d have a criminal record.
Here’s some technical stuff about chocolate intoxication of cats and dogs by Sharon Gwaltney-Brant, DVM, PhD.
The toxic compounds in chocolate vis-à-vis cats and dogs are methylxanthines, specifically theobromine and caffeine. They cause methylxanthine toxicosis (poisoning in layperson’s language). Methylxanthines cause competitive inhibition of cellular adenosine receptors and they also inhibit cellular calcium reuptake. This increases the free calcium concentration and enhances cardiac and skeletal muscle contractility. This compound may also compete for benzodiazepine receptors within the central nervous system and inhibit phosphodiesterase resulting in increased intracellular cyclic adenosine monophosphate. Highly technical staff but if you are that way inclined you might find it useful.
Of the two, theobromine is the predominant toxic components in most chocolate products. Caffeine is present in much lower concentrations.
The ASPCA Animal Poison Control Center states that mild signs of chocolate intoxication in animals occur after ingesting 20 mg/kg of theobromine and caffeine. At 40-50 mg/kg severe signs occur including and seizures occur at 60 mg/kg.
1 ounce of chocolate per 1 pound weight of companion animal is potentially lethal. Methylxanthines can cross the placenta and pass into the milk. Therefore, unborn or nursing kittens can be affected by chocolate toxicosis in their mother.
The signs of chocolate intoxication or poisoning occur within 6 to 12 hours of ingestion. The first signs include polydypsia, vomiting, diarrhoea, bloating and restlessness. The signs progress to tremors, ataxia, polyuria, hyperactivity and seizures. Other symptoms include tachycardia, premature ventricular contractions, tachypnea, cyanosis, hypertension, hypothermia and coma.
The treatment for chocolate ingestion by a cat or dog is to: stabilise the animal and perform gastrointestinal decontamination and then provide supportive care. You control seizures with diazepam (Valium) or a barbiturate as required. The veterinarian will monitor cardiac status via electrocardiography and treat arrhythmias when necessary.
Decontamination is carried out via emesis or gastric lavage. Afterwards a vet will administer activated charcoal. Sometimes chocolate can coalesce inside the stomach forming a large mass. This may be difficult to remove or vomit up. This would occur with dogs.
The chart below shows you the relative amounts of methylxanthines in various forms of chocolate:
The bottom line is to see a vet asap. The information here is for guidance only and comes from an experienced veterinarian. I am not a veterinarian.
SOME PAGES ON TOXIC TO CATS: