We know that, for example, taking oral estrogens or non-bioidentical estrogens will increase the risk of blood clots. There are risks, and many people are exposed to them. When it comes to blood clots, that can include thrombophlebitis, pulmonary embolisms or strokes, among other things. That means it's important for it to be estradiol. It has to be bioidentical and delivered transdermally to avoid the risk of clots.
When we talk about progesterone and progestins, it's a whole thing. Progestins are responsible for the vast majority of demonstrated risks associated with hormone therapy. That makes it extremely important to use progesterone. Everything can be explained at the molecular level, if you like.
It's necessary to provide safe hormone therapy, and it's no coincidence that our own hormones are the safest. They're chemically identical.