This has been a bit of a stumbling block for me, because I wonder if taking DHEA would in actual fact sort out my low thyroid function, without the need for thyroid medication. (My DHEA is low, 0.19 (0.40 - 1.7). This worries me slightly, because how do I know I need both DHEA and NDT, or - how will I know which is helping the thyroid? Take one or the other, but not both at the same time? At the moment, I've just started taking DHEA.
Perhaps somebody could help my mushed brain out lol. I read it 4 times, before I could actually understand what I was reading 
thyroid-info.com/articles/m...
It says:
Q. You describe something called secondary or tertiary hypothyroidism, where TSH is below 1.5 and Free T3 (and possibly the Free T4 as well) is below normal. How does this differ from primary hypothyroidism? Are there different causes for these different types of hypothyroidism?
A. These are forms of hypothyroidism that are not directly due to the thyroid gland failing. Traditional viewpoints would classify this as pituitary or hypothalamus dysfunction. However, there are far more common reasons for this that tend to be primarily related to the adrenal gland. My experience has been that the bulk of individuals who have thyroid impairment with the new TSH criteria above 1.5, are in fact related to adrenal insufficiency. *****Other causes of thyroid dysfunction would be related to an impairment of the body's ability to convert T4 to T3 (the active form of thyroid hormone). This is generally related to depressed DHEA levels.***** However, one must be very careful to not use DHEA without first measuring levels of other hormones, especially testosterone. DHEA given as supplement can clearly cause more harm than good if it is not needed.
secondary hypothyroidism
Hypothyroidism - causes
Possible secondary hypothyroidism 
Test results - low cortisol and DHEA. 
What causes subclinical hypothyroidism?
