Upon use, Isaac consumes the item which releases a bunch of white powder on the ground, activates the I'm Excited!!! pill effect and 8 stacks of the Wavy Cap effect, and produces a flash card on screen that reads "OH NO...".
The I'm Excited!!! effect increases the game's speed for the room, and the Wavy Cap effect heavily distorts the screen while increasing Isaac's fire rate and lowering his speed. Clearing rooms will reduce the intensity of the Wavy Cap effect by 1 level.
If Isaac leaves Contraband behind on an item pedestal, leaving and re-entering the room will cause a Snagger to appear and immediately take the Contraband and flee off-screen.
Notes
The Dealer will not reward Isaac if he isn't holding the Contraband, so it is obviously more beneficial for Isaac to keep the item on hand until the next floor rather than consume it. Note that Isaac may have to leave his previously held active item behind in order to complete this task, unless he has Schoolbag which makes this more trivial.
This article is about the larger version of Contraband dropped by 
Fake Beggars. For the smaller version, see 
Small Contraband.
Wavy Cap effect, and produces a flash card on screen that reads "
Dealer who will reward Isaac with 2-3 items from the 
Drug Dealer item pool.
Snagger to appear and immediately take the Contraband and flee off-screen.
Schoolbag which makes this more trivial.
Thank-You Fossil: Causes the 
Car Battery: No effect when using Contraband.
Book of Virtues: Contraband does not create any wisp when consumed.
Damocles: The 
Chaos: Items dropped by the 
Lost Cork: Doesn't affect the powder created from using Contraband as it is not counted as creep, nor does the powder have any effect on enemies.
