What is the target level for thyroid stimulating hormone?
The aim of levothyroxine treatment is to make the patient feel better, and the dose should be adjusted to maintain the level of thyroid stimulating hormone within the lower half of the reference range,21 around 0.4 to 2.5 mU/l. If the patient feels perfectly well with a level in the upper half of the reference range, then adjustment is unnecessary. If persistent fatigue, somnolence, or subtle cognitive problems (forgetfulness, befuddlement) exist then it is reasonable to increase the dose by 25 µg daily, or on alternate days. Although an open label non-randomised study has suggested that titrating the dose of levothyroxine upward (often leading to suppression of thyroid stimulating hormone) is associated with improvement in wellbeing,22 this was not confirmed by a recent randomised control trial.23 A fully suppressed serum thyroid stimulating hormone level (<0.1 mU/l) should always be avoided.9 A low level (0.1 to 0.4 mU/l) may be acceptable in a younger person who does not feel fully
