I meant to say once you are on thyroid medication however, the TSH may be 1mU/L but you may still be suffering symptoms. :)
I'd just like to emphasize that TSH level is much less important than FT3 and FT4 levels, and symptoms are most important of all. TSH is a pituitary hormone, an indirect measure of thyroid function and subject to many influences other than FT3 and FT4 levels. FT3 and FT4 are a much more direct measurement.
Do you have a diagnosed thyroid condition or disease? Are you on meds?
For most people without a thyroid gland problem, the TSH will typically hover somewhere around the 1mU/L range. For instance, my sister's TSH is 0.9, my neighbour is 1.25 and my thyroid labs prior to Hashimoto's thyroiditis showing up was 1.4 or 1.5. Africian Americans have a very low incidence of Hashimoto's thyroiditis and have an average TSH of 1.18.
Once you are on thyroid medication however, the TSH may be 1mU/l but you are still suffering symptoms. You need to go by your symptoms and optimise both your free T4 and free T3 levels. But it is recommended to aim for a TSH of 1mU/L to start with.
***
"When we have a normal population data for serum TSH we need to log-tranform the values in order to get the familiar bell-shaped curve that defines a normal distribution. The normal range is usually quoted as about 0.4 - 4mU/L (millunits per litre), but the log transformation introduces one peculiarity - it moves the mean and median values for TSH down towards the lower end of the range - at about 1mU/L.
The upwards tail between 2 and 4mU/L is rather thin, and there is room for doubt as to whether values in this range are actually normal or not. The important point is that when normalizing TSH by treatment, our target (the mean and median) TSH value should generally be around 1mU/L. If we simply aim for TSH in the middle of the range, some individuals will remain under-treated."
- Prof Jim Stockigt. "Subclinical hypothyroidism or Mild thyroid failure: How important is early diagnosis and what treatment is optimal? Sigma Pharmaceuticals, March 2001. [Thyroid Australia, Thyroid flyer. 2:3, July 2001.]