A multivitamin is a dietary supplement containing a blend of vitamins and minerals. The most common multivitamin supplements contain vitamins A, C, D, E, and K, as well as the B vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B6, vitamin B12, and folic acid). Minerals in multivitamin supplements include calcium, phosphorus, magnesium, iron, copper, ...