@mahonlye
I believe that you may be confusing bioidentical progesterone and progestins, synthetic progesterone research and the various studies of one or the other.
This is easy to do because the FDA, for some confused reasoning, allows all progesterone, whether synthetic or bioidentical, to be called progesterone. This even though a synthetic progestin is chemically completely different from your natural progesterone and bioidential is exactly the same chemically.
But yes, synthetic progestin is tied to many problems. Studies suggest a small increased risk of Alzheimer’s with long-term use (5+ years), increased breast cancer risk, and potential cardiovascular events, particularly when started later in life for synthetic progesterone.
Bioidentical progesterone is not tied to these problems.
Bioidentical (micronized) progesterone is generally considered a safer alternative to synthetic progestins regarding cancer and cardiac risks, often acting as a protective agent for the endometrium. While some studies suggest it may help prevent dementia, findings are mixed, with benefits largely dependent on starting therapy near menopause. This seems to be tied to just the fact that fewer studies have been done.
I have a long list of studies, but this one seems to hit most of the concerns:
https://bcmj.org/articles/hrt-older-women-it-ever-too-late