My Girlfriend use to take them for probation drug tests, she would stop smoking on saturdays then take anywhere from 4000 to 5000 mg for 3 days, and she passed tests every wednesday. If you smoked a lot of pot for a long time it will take a week or more.You will also want to take some slleeping pills about 30 minutes before because the niacin will make you turn red and burn like HELLLLLL. You need to find 500mg tablets and make sure they dont say no flush because you need the flush.