First of all, it works, so don't let all the talk about it not working scare you. You'll be fine. I recommend the 500mg non timed release. I take one at a time with plenty of water as many times as I am reasonably able to in one day (between 3 and 6). Now, there are "timed release" niacin pills and regular ones. I prefer the regular, non-time released pills, simply because the "flushing" happens sooner than later so you can get the flush over with wherever you want. If they're not timed release, you have the ability to try and take them somewhere comfortable, (ie not work, school, around informers). Then the "flush" (only with non timed release) will come and go in about 30 minutes. On the other hand, I have found timed release niacin will make you flush randomly, perhaps several hours after taking it. I smoked every single day (all day) for almost two years, all the way up to five days before my first drug test and passed just fine. Your skin may turn blotchy red and hot, but this is normal and not painful, just irritating. Do not forget lots of water and a little exercise...maybe some gatorade the day of your test to boost electrolytes. Be weary of detox head shop drinks; you may pass the drug test but fail the "integrity checks" that determine whether your urine is consistent with that of human urine. No worries.
Niacin in larger amounts is dangerous and can cause liver & kidney problems. It also can cause you to have unusual results with urine tests and is not guaranteed to make you pass. Take Niacin with a full glass of cold or cool water. Do not crush, chew, break, or open an extended-release tablet or capsule. Swallow the pill whole. Breaking or opening the pill would cause too much of the drug to be released at one time. Niacin extended-release tablets and capsules contain higher strengths of the medicine than the regular tablets. Niacin can also be found in many fitness drinks.