Progesterone - does generic teva come from natural sources?

(this is copied from another post, but totally appropriate) My experience is that Prometrium is natural, plant-based and "bioidentical" to human progesterone. And it is expensive. The "generic equivalent of Prometrium" that my insurance company filled my prescriptions with synthetic (synthetic hormones are designed by drug companies and are foreign to the human body, unique in ways so they can be patented. The formula has been altered in a small way, an H or OH or C has been switched on the basic steroid ring). The insurance companies might love the savings, but my body HATED synthetic (originally marketed as Provera among others). My doctor now writes my prescription for Prometrium with the 'dispense as written' box checked so I do not get the generic synthetic substitution that saves the insurance company money and increases their profit. It isn't a quality issue, it is a chemical composition issue.

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It didn't work and within three months I was in the same condition as I'd been without the medication at all. Prometrium is my magic pill (I am not peri-, post- or menopausal yet, it was given originally after a reproductive endocrinologist identified a lower-than-appropriate in comparison to the other hormones, level of progesterone and I credit it with 'curing' migraines and carry a child to term). I am currently researching whether or not Progestan is bioidentical or synthetic.