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.
Progesterone has many important roles in maintaining good health.
Estrogen is still being produced by conversion of androstenedione in body fat. This is often sufficient when progesterone is added. Progesterone stimulates new bone formation. When progesterone is deficient, an alternative DHEA pathway is called upon to take up the slack. This leads to increased androgen production, which is the cause of the unwanted facial hair.