Most of them don't do shit, it's the water that will dilute yer piss to the point you can get by... you're better taking some Vitamin B (?), Niacin, and then chug water and cranberry juice before the test .. oh, and if you fail the drug test, you won't get your money back because when they request a copy of the paper that says you failed, they tell you they cant give you any money because the test detected an illegal drug.. all that shit is a scam targeted at stoners that are uninformed about how these things work but freaking because they found out they had a test (that in reality, they probably knew about for sometime or could have avoided) ...