Article:
D&D 4th ed: Addiction

How to deal with an addictive substance in D&D 4th ed?
The answer lies in the existing rules and examples of Diseases.
If we treat addiction as a disease, it becomes fairly simple to implement as an attack on the character's Will defense.

The Spice of Incredible Flavor (aka, Incredible Spice) traces it's origins back to the height of the empire of Bael Turath, where, it is reputed that a guild of bakers made a pact with infernal powers, and as a result, the products of their baking were so sought after, armed guards delivered them across the entire continent.

The secret of it's manufacture was closely guarded of course, but as with anything that paves the way for such grotesque profits, it was a secret that saw many attempts to steal it away, and in some cases, these attempts succeeded.

The empire is gone, it's ruins lie covered by the soil of time, but the secret of the spice lives on.

The principal ingredient is the foul but sneaky little Delicious Pink Slime, and a complicated, expensive and exacting ritual which yields around a pound of the pure spice.

One aspect of the spice which has prevented it's widespread distribution as a product in and of itself, is that it can slowly convert any other fine spice, added in one part per five, to create more of the Incredible Spice (a property that reveals it's infernal origins, according to the sages).

With a pound of spice and moderate control of it's consumption, the supply can be extended forever.

Of course, every marvel has it's down side, and in the case of the Incredible Spice, it lies in just how effective the spice is at it's task. 

The eating of any food which includes the Incredible Spice includes an attack against the target's Will, if the attack beats the target's Will defense, they now have an addiction to the Incredible Spice, a disease that they can try to beat with an Endurance check each time they have an extended rest (this is the Improve, Maintain or Worsen track on the diagram below), in addition, the condition of the disease causes them to use more of the addictive substance, so, based on how addicted they are, the target will be making more frequent and difficult endurance checks, as they use more of the addictive substance and get deeper and deeper into the addiction spiral.