Chocolate can produce a stimulant effect and lead to feelings of nervousness and anxiety in some people. It is also a common food allergen. Chocolate, along with red wines and aged cheeses, has been linked with nervous tension as well as migraine headaches. All of these foods contain compounds known as vasoactive amines, which can dilate brain vessels, triggering headaches in susceptible individuals.
Since chocolate contains oxalic acid, a compound that can bind to calcium in the urinary tract to form kidney stones, dark chocolate should be avoided by individuals prone to kidney stones. According to a study conducted in Brazil, while consumption of dark chocolate caused a 20 percent increase in urinary oxalate excretion, no such increase was observed in the group receiving milk chocolate, suggesting that as long as enough calcium is also present, it will bind to oxalates in the gut, preventing the formation of kidney stones.
Chocolate is a food high in arginine, an amino acid required by the herpes virus to replicate. Chocolate and other arginine-rich foods should be avoided by those with active and frequently recurring herpes infections. Chocolate does not contain goitrogens or purines.