I began taking Niacin in pure powder form back in 1984. Small amounts at first - slowly and gradually increased until I got to my desired dosage.
I’ve found that the flush effect is diminished greatly by taking an aspirin tablet 20 minutes beforehand. Actual aspirin, not Tylenol or Advil, The low dosage aspirin worked for me.
Start low and slow.
Were you taking it for cholesterol?