I am working with a person who doesn't experience flush from niacin. First day, my coworker took 500 mg, it didn't work, she too 500 mg more, it began to work. She had flush around 2 hours, which followed by dizziness. (Also redness around 8 hours) The second day, she took 500 mg and had normal reaction for niacin. The 3rd day, she took 3 g niacin (1g powder and 2g in pills) and did not work at all. I took from the same bottle half of tablets(around 250mg) and it worked pretty good. Maybe, some one had the same experience or some clue?