What amazed me about the relationship between Hypothyroidism and testosterone: For decades I had trouble with muscle development. I have been using synthroid for my Hashimotos Hypothyroidism. I recently switch to Naturethroid (a natural bio-identical hormone replacement,) and within 8 weeks, my muscles began to grow! I don’t think that changing from synthetic to natural analog was as much to blame for the growth as was the serendipitous increase in Free T3. I have a conversion problem that kept me from converting the T4 into T3. The Free T3 levels had always been within a “normal” range but at the bottom third of that range. Titrating The Naturethroid, which contains T3 as well as T4, to achieve Free T3 levels in the upper third of the range changed everything. I’ve not checked Free testosterone, but anecdotally — dramatic muscle increases globally, and oddly enough my voice decreased into a deeper tone. Overall more cheerful and clear headed.