Riboflavin is biologically inert and must be converted into active coenzyme derivatives. Since hormones regulate this conversion, riboflavin deficiency may result from disorders in hormonal control of vitamin metabolism or drug effects, as well as from inadequate dietary intakes. Factors regulating riboflavin metabolism include thyroid and adrenal hormones. Riboflavin deficiency may be associated with use of oral contraceptives and chronic alcoholism. Phenothiazine derivatives competitively inhibit coenzyme biosynthesis, promoting riboflavin excretion. Boric acid complexes with riboflavin, producing riboflavinuria. Phototherapy of newborns in treatment of hyperbilirubinemia may cause decomposition of light-sensitive riboflavin. Thus, endocrine disturbances and pharmacological agents may adversely affect riboflavin metabolism