I had a player who wanted to become a drug king pin in a D&D game so he asked me to design 'D&D crack'. I took up the challenge and, with the help of a good friend of mine, came up with the Substance. It's very useful for adventurers who have the money to keep up the habit, but anyone else will become a twitching crack fiend, sitting in their own filth and screaming incoherently. It's harsh but the benefits will get your party hooked and you can use it to make them do whatever you want...muhahaha
Fast Healing 1 for 24 hours, heal mundane disease 24 hours, immunity to mundane disease 24 hours, +1 on all saves for 24 hours.
Fort dc25 to avoid addiction
Two successful withdrawal saves in a row kicks the addiction.
Every successful withdrawal check grants 24 hour reprieve from current stage symptoms (but not previous)
Stage 1 after 24 hours: Mild head aches and muscle aches
(3 days, withdrawal check fort DC23 every day) permanently sickened for duration of withdrawal. (sickened: -2 on attack, damage, saves, skill checks, and ability checks)
Stage 2 after 4 days: Above, plus nauseous and occasional vomiting and diarrhea
(3 days, withdrawal check fort DC21 every day) at start of combat or once every 4 hour out of combat Fort save DC21 or become nauseated for 1d4 rounds. (Nauseated: unable to act except 1 move action per turn)
Stage 3 after 7 days: Above, plus increasingly severe head aches and muscle aches
(3 days, withdrawal check fort DC19 every day) 1 point of ability damage across the board per day up to 3.
Stage 4 after 10 days: Above, plus weeping migraines
(5 days, withdrawal check fort DC17 every day) Will save DC17 or dazed every round. (Dazed: entirely unable to act, no action what so ever)
Stage 5 after 15 days: Above, plus pain induced madness
(5 days, withdrawal check fort DC15 every day) will save 15 or go insane. (Insanity: Roll d% every round 01-10 attack self, 11-20 act “normally”, 21-70 babble incoherently, 71-00 attack nearest person or creature.)
Stage 6 after 20 days: A single Fort save DC13 or instant horrible, screaming, shitting death over the course of five minutes.
At any time during withdrawal if the Substance is consumed again the subject goes back to the initial addiction phase, failing the check automatically, but all negative withdrawal stages are instantly gone.