Antithyroid drugs are molecules known as thionamides that inhibit thyroid hormone synthesis by interfering with thyroid peroxidase mediated iodination of tyrosine residues in thyroglobulin. These extensively used drugs are associated with a variety of well-known side effects such as anti-neutrophil cytoplasmic antibody (ANCA)-positive vasctilitis, granulocytopenia and aplastic anemia.