High Quality Content by WIKIPEDIA articles! Megavitamin therapy is the use of large doses of vitamins, often many times greater than the recommended dietary allowance (RDA) in the attempt to prevent or treat diseases. It is typically used in complementary and alternative medicine by practitioners who call their approach "orthomolecular medicine", but also used in mainstream medicine for "exceedingly rare" genetic conditions that respond to megadoses of vitamins. In 2002, a review of these conditions identified about 50 that respond to "high-dose vitamin therapy". Further understanding of these conditions is expected to play a part in the emerging field of nutrigenomics.