Phytoestrogens in Reosto inhibit bone resorption (breaking down of bones). Reosto also negates the bone resorptive effects of parathyroid hormones and prostaglandins. The drug is rich in elemental calcium, which helps in better bioavailability of the mineral. This allows the optimum amount of mineral to be absorbed into the bone. Reosto stimulates bone formation and prevents the risk of osteoporotic fractures.