I just found out that I have to take a drug test on the 21st of December. The last time I used marijuana was on Tuesday, the 1st. I am thinking about taking 500mg of Niacin daily until about 3 days before the test and drinking a whole bunch of water. Will this work? Also, I'm 6'8" 245 lbs. I also have only smoked 3 times in the past 3 weeks, and before that I was clean for about 4 months.