Niacin deficiency can cause diarrhea, memory loss, red/swollen tongue, and red, flaky skin. Niacinamide (nicotinamide) is a form of vitamin B3 (niacin) and is used to prevent and treat niacin (pellagra) deficiency. Niacinamide is often used instead of niacin because it causes fewer side effects (eg, flushing).