Yes, caffeine is considered a stimulant and therefore addictive. I have also recently learned that, as essiheart stated previously, MSG is added to many, many processed foods to make it taste better, and can be disguised under alternate names such as yeast extract, textured protein, protein isolate, and calcium caseinate to name just a few.
This is a very dangerous and potentially life threatening additive and one to be avoided at all costs.
To learn more, read Dr. Russell L. Blaylock's book "Excitotoxins, The Taste That Kills".
I believe that anything added to a food that has a physical effect on the way you feel (chocolate is a perfect example) can be addictive if not eaten in moderation.
All the more reason to eat right and read those labels!