Hi, I have a thyroid condition but is mainly underactive thyroid due to Hashimotos, I personally haven't had any problems with milk supply but my thyroid level has been kept in check with thyroxine - however I recently read a book called The Breastfeeding Mother's Guide to Making More Milk By Diana West, Lisa Marasco to review for ABA library and it had a section in it about the contribution of hormones - there was a specific passage about thyroid issues - unfortunately I have given the book back to the library or I could read up the info for you - but maybe someone else has the book who could help? Also segments of the book are available on google books - but unfortunately the page about hyperthyroidism isn't there only the ones on hypothyroidism (pg 130) and post partum thyroiditis (pg132) - if you put "making more milk - thyroid" in Google, the google books link should come up as one of the first.