Niacin doesnt work. Neither does Goldenseal. Heres what does:
Supplement Why you take it
B Vitamins (lots) - Water soluable, keeps your piss NEON yellow, even when you dilute your urine
Creatine (any form) - Even if your piss is yellow, they can tell if its diluted or not based on your creatinine ratios. Supplemental creatine will prevent them from seeing you diluted your sample.
Water (minimum 1 gallon the day of the test) - You're simply trying to temporarily dilute your urine as much as possible. What you drink in the days leading up to the test doesnt matter.
Other potentially beneficial info:
Dont use the start of your piss stream. Start in the toilet, fill the cup after a few seconds, then finish in the toilet. The start and end of your piss are the most dirty parts.
Niacin, Goldenseal, Certo (fruit pectin), Cranberry extract, etc. do nothing to help dilute your urine. Cranberry extract may make you piss more before the test.
The day of the test, try not to eat anything before the test unless its some fat.
THC is fat soluable and a little olive oil/fat on an empty stomach may help.
THC has acceptable cutoff levels (ng of THC per mL)
However, the other drugs tested for may be a Yes/No instead of having a cutoff
Alcohol is eliminated at roughly 1 shot per hour, so dont get drunk the day before the test.
MDMA/Ecstasy use will lead to a positive test for Amphetamines.
(As will ephedrine, Pseudoephedrine, PPA, Ephedra, etc.)