It supplements the estrogen your ovaries are no longer producing in quantity, which steadies the systems estrogen helps regulate: temperature control, the tissue of the vagina and urethra, bone turnover and sleep architecture. Progesterone is added where there is a uterus to protect.
Where it acts
Austin patient guide: four systems, one hormone
Temperature is the clearest of the four systems to explain to a Austin patient: the band the brain defends narrows as estrogen falls. The hypothalamus regulates body temperature within a narrow band, and estrogen influences how narrow. Restoring it widens the band again, which is why hot flashes respond so well.
The tissue of the vagina and urethra is dense with estrogen receptors. Restoring estrogen thickens it, improves blood supply and restores lubrication, though systemic doses do not always reach it adequately.
Bone is in constant turnover between cells that build and cells that break down. Estrogen restrains the breaking-down side, which is why its withdrawal accelerates bone loss and why replacing it prevents that. Related reading: patient guides, bone health and osteoporosis and vaginal estrogen go further into it. Of the four, bone is the one a Austin patient will never feel changing, which is why it belongs in the decision rather than the follow-up.
