use a parallel process event that checks a variable. if the value of the variable is high enough for the character to be addicted add some sort of status effect to do what you want it to do. and if the variable drop below the threshold remove the effect.
then make another common event that isn't parallel process and have the item that caused the addiction call the event. have the even increase the variable that the parallel process event is checking. each time the item is used the event will be run and add the the variable which will represent the number of uses of that item.
you can even make it more complicated and have the parallel process event reduce the variable after a certain amount of time has passed if the character isn't already addicted so that if you string out the uses of the item you won't get addicted.
you could add a second variable that increases over time when the player is addicted and the higher the value the greater the effects of withdrawal. usage of the item while addicted would decrease the withdrawal variable.
removal of the addiction is as simple as creating an item with a connected common event or another situation like a doctor event that reduces the usage variable provided you've set up the parallel process event to remove the addiction when the usage variable drops below the addiction threshold like I said earlier.
you can also set it up so that the addiction wears off if the withdrawal variable gets too high if you want.
This is just a general overview of the principles behind creating the event system. it's fairly easy but if you need help on specific parts ask and we'll help. most of use really don't have the time to make it for you. so expect to do most of the work yourself.
also If i don't get leveled up for providing such a good process description for you I'll be very disappointed, you won;t like me when I'm disappointed