“…Yet when thiourea derivatives had been found to inhibit thyroid activity in animals, thiouracil was widely used to control hyperthyroidism in Man, either to avoid the need for subtotal thyroidectomy, or at least to restore the thyroid activity to normal at the time of operation. Within a few years ofits introduction, however, three reports (2,3,4) had appeared, which showed a mortality from agranulocytosis of 0.4 per cent of patients treated with thiouracil; a risk 25 times greater than Girdwood's highest value. If safer and equally effective derivatives of thiourea had not rapidly become available, the problem would have.…”