I have mixed feelings on this. A guy where I work smokes as he puts it "every weekend" and then every Monday does the whole Niacin thing. We recently got randomed, and he told me to do the niacin thing and I did. I also combined that with drinking a shit-ton of water and I smoke every day, multiple times a day sometimes. We both passed. Whether it is that my job just does not care about weed, or by some miracle we both passed, I have no idea. I personally do not think it works. You are much better off diluting (there is a great how to pinned in this forum) or substituting either with synthetic or clean urine.