Why are we having this conversation at all? Is there something that makes chocolate toxic? The cocoa bean, from which chocolate is made, contains a substance called theobromine, which is a plant alkaloid with a slightly bitter taste (other plant alkaloids include America’s favorite, caffeine, as well as cocaine, nicotine, and the effective chemotherapy drug Vincristine). In the human body, theobromine is, at most, a mild stimulant, acting similar to caffeine. Theobromine is also a vasodilator, meaning it can open up your blood vessels and cause your blood pressure to drop. It’s also a diuretic, so you could feel the urge to urinate more often.