Thioamides have been used in the management of hyperthyroidism for over 50 years. Liver dysfunction is a rare but important side effect associated with their use. Recently, cases of liver failure associated with propylthiouracil have prompted the Federal Drug Administration to issue a Boxed Warning to the label of propylthiouracil regarding its risk of potentially fatal liver injury and acute liver failure in adults and children. Herein, we present a case to underline the importance of recognising the similar potential for severe hepatic dysfunction with the use of other thioamides.