Hi Diane, What an interesting question. I can’t say that I have an answer, but I will tell you that with POTS, we certainly get worse with estrogen! Any vasodilator (like estrogen) or HISTAMINE (as in mast cell disease) causes us to feel much sicker, usually. Many of us stop our periods to get by (I stopped my period for 2 years). That helps a lot of us. Progesterone can cause vasoconstriction of the arterioles, which could bring less oxygen to our tissues (including our brains). I don’t believe researchers have it all sorted out yet (as evident by the conflicting articles that we read! What’s a woman to do?). Does anybody else have any thoughts on this? Thanks for a great question! 🙂 Diana