Question: are high doses of niacin dangerous?
Answer: Niacin flush is harmless. However, high doses of niacin can cause other, more dangerous side effects, although these are rare (20). The most harmful of these is liver damage. High doses of niacin may also cause stomach cramping, so don't take them if you have a stomach ulcer or active bleeding ( 9 , 21 , 22, 23 , 24 ).