The action of progesterone, on the one hand, is based on blockages of estrogen receptors,as a result of which the absorption of fluid from the tissues improves, the compression of the milk ducts decreases; on the other - blocking the prolactin receptors in the breast tissue, which leads to a decrease in lactopoiesis. Thus, the local use of the drug, creating a high concentration of progesterone in the area of application, does not have a systemic effect and avoids undesirable side effects.
The mechanism of action of the Projug is based on an increase in the concentration of progesterone in the tissues of the breast. The active component of the drug is progesterone. Progesterone reduces the expression of estrogen receptors in the tissues of the mammary gland, and also reduces the local level of active estrogens by stimulating the production of enzymes (17β-hydroxysteroid dehydrogenase and estrone sulfotransferase), oxidizing estradiol in a less active estrone, and then, binding the latter, turning it into an inactive estrone sulfate. In this way, progesterone limits the proliferative effect of estrogens on breast tissue. Also progesterone has a small sodium diuretic effect due to inhibition of tubular reabsorption and increased cell filtration,thereby preventing fluid retention in secretory transformations of the glandular component of the mammary glands and, as a consequence, the development of pain syndrome (mastalgia or mastodynia). Along with this, the transdermal way of introducing gestagens also allows to influence the condition of the glandular epithelium and the vasculature, as a result of which the capillary permeability decreases, and, consequently, the degree of edema of the breast tissue decreases and the symptoms of mastalgia disappear.