i always take alot of niacin if i know i'm going to have to piss in a cup. alot of people claim that it doesn't work...
but i've passed 4 drug tests with the shit...
and once.. i had smoked the morning of the test...and took 7 (100mg) niacin pills and downed about a gallon of water somewhere around 20 minutes before the test. so i DO believe that it works. doesn't hurt to do a little sweating either.