Niaspan, the brand name form of niacin, is a prescription medication used to lower high cholesterol and fats in the blood. Niaspan is a B-complex vitamin, which may work by increasing the breakdown and removal of certain fats in the blood. This medication comes in tablet form and is usually taken once daily at night after a low-fat snack. Common side effects of Niaspan include warmth and redness of the face, rash, diarrhea, and nausea.