Niacin is a myth. It does nothing to help pass a U/A. Besides, taking considerably more than the 15 mg RDA can have some serious health consequences..

Misusing Vitamin To Foil Drug Test May Be Toxic; Plus, It Doesn't Work

http://www.wired.com/wiredscience/20...rons-overdose/

Drinking copius amounts of water in the days or weeks before the U/A is of no help. It must be understood that THC is not water soluble unlike other types of drugs. THC is fat soluble. Therefore, you cannot rid the body of THC by drinking copius amounts of water. Does not work that way (more on that in a moment).

THC is stored in the fat cells and remain there until the fat cells are burned for energy. When fat cells burn, the THC metabolites are released back into the bloodstream. The kidneys filter the THC metabolites from the bloodstream and are deposited into the bladder for the eventual exit. The rate in which the THC metabolites are filtered from the bloodstream by the kidneys is unaffected by copius fluid consumption.

The purpose of drinking fluids is to dilute the THC metabolite concentration that is present in the bladder. The idea is to dilute that concentration enough to where the urine sample registers below the cutoff thresholds of the drug screen. This dilution phenomena, however, is only temporary - once the fluids ingested had all been urinated out, the bladder is replenished with fresh THCA-laden urine and thus the donor is right back to square one. Therefore, drinking fluids is only helpful on the day of the U/A.