Hypothyroidism is a very common medical condition. Most patients symptoms improve with standard thyroxine treatment, however some do not. There are some genetic variations that leads to poor conversion of T4 to T3 (the active thyroid hormone).  It is not always possible to tell from TSH and T4 chemistry that this issue is present. This podcast covers a review article published in the Lancet in 2023. 

If you have an underactive thyroid and are taking thyroxine but have hypothyroid symptoms despite apparently 'normal' TSH and T4, especially if you struggle to lose weight and have raised blood cholesterol then it is possible that your T4 to T3 conversion is impaired and T3 supplements may make you feel a lot better. 

The relevance of T3 in the management of hypothyroidism