I took 26 Niacin the day before my test although it wasnt a full 24 hours as everyone says your suppose to take it before the test. I showed up positive with PCP and Marijuana even though I took them. Has anyone THEMSELVES passed a UA (honestly) using Niacin? If so, please give full details on how to use Niacin. NOTE - I used regular old Niacin 500mg tablets. It wasnt time release.