Tag Archives: methylxanthines

Theobromine and Friends

Theobromine is to chocolate as caffeine is to coffee. Both, plus the theophylline in tea, are notable stimulants from the same chemical family, the methylxanthines. They have many effects on humans, but they’re best known for suppressing drowsiness—as anyone who has had a shot of espresso in the evening will know.

a chemical line drawing representation of a theobromine molecule
A theobromine molecule

Theobromine is a key part of chocolate’s molecular signature, occurring in only a handful of plants (tea, yerba mate, kola nuts, and a few others). Cacao also contains caffeine, so archaeologists look for the two together when identifying ancient Mesoamerican pottery that may have contained chocolate. Theophylline (the characteristic methylxanthine in tea) is present in cacao as well, though its concentration depends on the variety.

All methylxanthines are stimulants, but they may have slightly different effects. Caffeine, especially in large doses, tends to leave you wired and jittery. Theobromine has a weaker effect on the nervous system. It lowers blood pressure, which may be why chocolate is known for inducing general happiness. Theobromine’s stimulant effects may also be partially responsible for chocolate’s reputation as an aphrodisiac. Theophylline—present in cacao, but more often associated with tea—tends to increase blood pressure, and eases breathing. While the amount of theophylline in a cup of tea is too small to have a noticeable effect, in higher concentrations it is used to treat asthma and other respiratory diseases.

In addition to its role as a stimulant, theobromine has an effect on the respiratory system similar to that of theophylline. It has recently been tested as a cough suppressant, though theobromine-based cough medication isn’t yet available in most of the world. An initial trial suggested theobromine may actually be better than codeine as a cough suppressant, but there were only ten test subjects. The dose tested was around 1000mg, which you can get from as little as fifty grams (two ounces) of dark chocolate, depending on how it is processed and prepared. Full-scale clinical trials have been completed in both South Korea and the UK, but the results are not yet available. In early 2016 we checked with the lead researcher, Professor Alyn Morice, who said they are waiting to publish until the medication is ready to go before regulatory bodies.

Theobromine has one other notable effect: given a high enough dose, it is poisonous. While it’s usually very difficult to get a lethal dose from eating chocolate, people with certain genetic conditions may be far more susceptible. Other animals are much more suceptible to the effects of theobromine. It’s been used to poison coyotes and dope racehorses. It definitely affects dogs, cats, birds, pigs, and cows. Plenty of people have a dog who has gorged themselves on Hershey’s Kisses, but it doesn’t mean the dog is immune. It’s actually a reflection of the low cacao content in commercial milk chocolates. That same dog could be in serious trouble if they get their paws on a bar of 70% dark. Initial symptoms of theobromine poisoning include nausea and vomiting, as well as diarrhea, but severe cases can lead to seizures and heart attacks.

Dose that would kill 50% of dogs (LD50) Lowest dose known to have a toxic effect on humans (TDL0) Daily dose that is known to have a substantial negative effect on humans
Pure Theobromine 0.005 oz/lb 0.0004 oz/lb 0.016 oz/lb
Raw Cacao 0.16–0.32 oz/lb .01-.02 oz/lb 0.5–1 oz/lb
Dark Chocolate 1 oz/lb .09 oz/lb 3.5 oz/lb
Milk Chocolate 3 oz/lb 0.27 oz/lb 10 oz/lb

Table 1: Theobromine Poisoning Dosages

Based on the dosages in Table 1, some simple math tells us how much chocolate you (or your dog) would have to eat to be affected. Dosages are described by the quantity of poison per pound of body weight. Given, for example, the dose of dark chocolate needed to have a substantial effect on most people (3.5 ounces per pound) we can multiply by the weight of the average human (137 pounds) to determine that they would have to eat 477 ounces of dark chocolate, on a daily basis, to meet that level. Someone with a low tolerance for theobromine, however, could experience some effects after consuming only 12 ounces of dark chocolate—several large bars. It takes even less raw cacao to have the same effect. Milk chocolate’s theobromine content is about one third that of dark chocolate, so it takes far more to have a comparable effect.