http://www.ironcrown.com/ICEforums/index.php?topic=9234.msg119318#msg119318
Here is my system. I basically treat it like a "fumble". As was pointed out, it might be a little backwards on the normal RM rules, but it's a lot easier for me; less rolls/charts/page turning involved.
Everything is based on AF. AF determines how long withdrawl lasts, hits taken when you can't get your fix, what happens if you get your fix while "jonesing" etc.
This works for drugs, spells, whatever you think could be habitual.