Progesterone's role in the body is closely linked to that of estrogen, in that in many ways it opposes the action of estrogen. In fact, many receptors in the body can be occupied by either hormone. When progesterone is occupying an estrogen receptor, the action that estrogen would cause if it were there instead can be blocked. For every receptor that is occupied by progesterone, a molecule of estrogen is thus freed up to do its work elsewhere. In other words, putting progesterone into the system effectively raises the amount of estrogen available to do estrogen-only tasks. This is why there is often a noted increase in Oestreogen Dominance when first starting Progesterone Therapy.