Beans from the Cacao Tree, Theobroma Cacao, are the source of the world's chocolate. The Principal Alkaloid of the Cacao Bean is theobromine, a close structural relative of caffeine. Theobromine differs from Caffeine by only one Methyl group.

Cacao contains between 1.5-3% Theobromine and 0.2-0.4% Caffeine. Theobromine is a minor constituent of tea but it is not present in coffee. Theobromine has a ten fold less stimulating effect to humans than caffine does. For dogs however, 100-200 mg of theobromine per kg of a dogs body weight can cause Cardiac and Central Nervous System distress. The average value of theobromine in Milk Chocolate: 200mg per 100g, Unsweetened Baking Chocolate: 1400mg per 100g, Cacao: 2600mg per 100g

The Aztec emperor Montezuma used to drink a goblet of chocolate before entering his harem each night, leading to the popular legend about Chocolate's Aphrodisiac Properties. But this legend may just have some truth to it... Chocolate contains three substances, caffeine, theobromine and phenyethylamine that might be related to this myth. Caffeine acts as a stimulant. Theobromine stimulates the heart muscle and the nervous system. Phenyethylamine is reputed (no conclusive proof exists yet) to be a mood elevator and an anti-depressant. The combination of these three substances, giving you extra energy, making your heart beat faster, making you a bit jumpy and slightly giddy....well, you can see how chocolate could be linked to love. But before you go out to buy several cases of chocolate to ply your lover with tonight, remember that these substances show up only in small quantities in chocolate.

Formal Chemical Name (IUPAC)
3,7-Dimethyl-Zanthine,2,6-Dihydroxy-3,7-Dimethyl-Purine