The -blam!- are you talking about with caffeine. Caffeine is technically addicting but all it does is block receptors in your brain that tell you to be tired or to sleep, and the only side affect of going from 10 cups of coffee a day to none (quitting cold turkey) would be a head ache and maybe but probably not, an upset stomach for a day.

I've never heard of an incident that involves alcohol and harder drugs, but yeah, it could be viewed as a gateway drug.