Progesterone is not found in any plant. Natural progesterone is synthesized from fat saponins such as diosgenin from Mexican wild yam or from soy. What Your Doctor May Not Tell You About Menopause, by John R. Lee, M.D., Warner Books, 196. Progestins do not convey the full spectrum of progesteron's benefits as listed above and they have numerous potential deleterious side-effects not found when using natural progesterone. The natural hormones are more quickly metabolized and excreted than the synthetic versions.
Progesterone has no known side effects.
Pharmaceutical progestins do not appear in the biosynthetic pathway. The fact is, they are not found in any living forms. Furthermore, being foreign to all living things, they are patentable and thereby potentially more profitable. Many of the symptoms of PMS are consistent with estrogen dominance due to relative progesterone deficiency, which can be corrected by progesterone supplementation. Essentially no progesterone is made by the ovaries after menopause.