Dibromotyrosine is a brominated derivative of a natural amino acid tyrosine. In the human body, dibromotyrosine is produced by eosinophil peroxidase secreted from activated eosinophils. Dibromotyrosine is naturally produced by marine sponges. Dibromotyrosine is used in medicine for the treatment of functional hyperthyroidisms. It acts by competing with iodination of tyrosines, thus reducing the active form of the thyroid hormones. Dibromotyrosine also appears to maintain the ability to control TSH production through negative feedback on the pituitary gland, reducing the biological activity of the thyroid. Dibromotyrosine is marketed in Italy under tradename Bromotiren.