The main test for the diagnosis of hypothyroidism is to check the level of TSH (thyroid stimulating hormone). TRH tests help in distinguishing whether the disease is due to pituitary dysfunction or the hypothalamus.
Usually hypothyroidism requires a lifetime of drug therapy like Leyothyroxine (T4). T3 (cytomel) is also used but T4 is found to be more successful then T3 as T4 is a more stable thyroid hormone than T3. T4 replacements are taken in the morning before having breakfast.