In Britain the drug first used is carbimazole or, if side-effects occur, propulthiouracil is the second choice.
Side-effects of carbimazole are uncommon. The most serious side-effect is extremely rare and is due to a lowering of the number of white blood cells. You would recognise this by the development of a sore throat or ulcers in the mouth, in which case you should immediately stop taking the tablets and report immediately to your doctor who will check the level of white cells in your blood.