I've seen many posts in various threads on these topics, but would like to consolidate a discussion here. I found out last year that while my estrogen is fine, my progesterone is off the charts low. That's after coming off ~27 years on the pill... I started taking 100mg oral progesterone/day (bioidentical), on Day 8 through Day 1. After about six months, my progesterone number was still low. Granted, my periods are starting to get wacky (e.g. I've already had 11 so far this year, yikes!), so it's hard to tell exactly when Day 19/20/21 is, and sometimes I don't even make it that far before my period starts. I upped the dose to 200mg a few months ago. Since my sister has Hashi's, I've had regular thyroid tests for many years. I do not have Hashi's myself; however, I have had elevated rT3 (at times, highest number at the top of the range), and on my most recent testing, low free T4. And have had low body temps for as long as I can remember. I was thinking my low progesterone was causing the thyroid issues, my doc thinks it's the opposite (thyroid causing low progesterone). He wanted to start me on Synthoid, but I demanded Armour (and later found papers suggesting that there is a certain SNP (for which I'm hetero), folks with it do better on T3+T4 than plain T4. Now that I'm on 200mg progesterone, I'm starting to get up over 98.0, even to 98.6 some days. I've noticed that my temp seems to track with the progesterone, regardless of whether or not I'm taking Armour. I'm interested in hearing whether folks think low thyroid leads to low progesterone, low progesterone leads to low thyroid/low thyroid symptoms, or something else.