Niacin, also known as nicotinic acid or vitamin B3, is a water-soluble vitamin whose derivatives such as NADH, NAD, NAD+, and NADP play essential roles in energy metabolism in the living cell and DNA repair. The designation vitamin B3 also includes the corresponding amide nicotinamide (or "niacinamide"), whose chemical formula is C6H6NO2.
Other functions of niacin include removing toxic chemicals from the body, and assisting in the production of steroid hormones made by the adrenal gland, such as sex hormones and stress-related hormones.