NOW Niacin, Double Strength, Flush-Free, is a nutritional supplement. Niacin (Vitamin B-3) is an essential B-complex vitamin. Flush-free niacin contains inositol hexanicotinate, a form of niacin that consists of six molecules of niacin linked to a single inositol molecule. It is slowly broken down in the body to yield free niacin and inositol. This gradual release of niacin allows for true niacin activity without the characteristic niacin flush that many people cannot tolerate.