And then you have the mental side, where your own psyche is ingrained with the feelings you had while on it. This is often the worst part as it worms into your subconscious, most noticeably with smokers that tend to for years after quitting still have a need to play with things with their hands or put something in their mouth. Your consciousness has drilled into you that you need it to be normal, not that you actually do physically, but you -think- you do.
So the idea I had is, why not have that reflected in SD? The first stages of addiction grip your character, reflected by a 'physically addicted to ...'. Sure, if you quit taking the drug you'll start throwing up or doing twitches and tweaks ecetera so forth.
But then if you decide to keep going at some point you trigger 'mentally addicted to ...' and bam, this is when people start flipping out without it. You're driven to do things you'd never do in your rational mind. You'd even -kill- people to get your drug of choice even if you've never been violent in your whole life.
