I hadn't been aware of that, as far as I remember. However, the niacin that does not cause flushing is basically ineffective for improving blood flow or for helping someone who has or is inclined toward a lupus diagnosis. Perhaps other common uses of niacin also are ineffective when it does not cause flushing. For some, it might not make any difference, I don't know.
So much to know! There are several types of magnesium, all important. There are combinations and amounts of supplements one should not do. Vitamin B's work better together....
@Jeff Elohim "Nicotinamide (NAM) is a form of vitamin B3 found in food and used as a dietary supplement and medication.[3][4][5] As a supplement, it is used by mouth to prevent and treat pellagra (niacin deficiency).[4] While nicotinic acid (niacin) may be used for this purpose, nicotinamide has the benefit of not causing skin flushing.[4] As a cream, it is used to treat acne." See: https://en.wikipedia.org/wiki/Nicotinamide