Hello and welcome to Healthcare Magic. Thanks for your query. Neo-Mercazole (Carbimazole) is used in the treatment of hyperthyroidism. The drug is permitted to be used during pregnancy, but needs to be taken in the minimum effective dosage. High doses can have a risk of causing neonatal hypothyroidism and goitre. In very rare cases, there is possibility of a congenital abnormality called aplasia cutis in neonates. If dose is in the minimum range and the thyroid status of patient is regularly monitored, there is no major effect on the unborn baby. In fact the possibility of congenital malformations in babies born to untreated mothers suffering from hyperthyroidism is more than those treated with Neo-Mercazole. Inderal (Propranolol) has been assigned to pregnancy category C by the FDA. This means that some animal studies using high doses have revealed evidence of embryotoxicity, but there is no evidence of embryotoxicity in humans. In case you suspect that you could be pregnant then you can start off folic acid supplements right away. Further decisions regarding your thyroid medication can be later discussed with your endocrinologist. Wish you all the best. Regards, Dr. Jonas Sundarakumar