The average chocolate bar contains a quarter as much caffeine as a cup of coffee.
Some people complain of headaches and migraines after eating chocolate. These are not signs of true food allergy, but may be due to a food intolerance or sensitivity. Genetics, lifestyle, medications, and hormonal changes can make headaches and migraines more severe. But caffeine, even in high doses, has not been shown to cause heart attacks.
Many people say that they are allergic to chocolate, but a true chocolate or cocoa allergy is rare and difficult to prove. Chocolate is sometimes blamed for allergies caused by other ingredients added to chocolate during processing, including corn syrup, lecithin, gluten, and nuts. See a board-certified allergist if you suspect that you have a food allergy or sensitivity.