hi, A poorly controlled asthma means poor prescription or constant exposure to allergens. Seretide contains steroid and bronchodilator whereas Flixatide contain only steroid. It is unlikely that flixatide is going to be a better option. If symptoms are not under control you need dose escalation and some oral drugs also. there is no significant harm in using these in thyroid patients, keeping in mind that asthma control is much more important. A consultation with a good pulmonologist is all that you require. all the best.