Increased bone formation in the absence of accelerated resorption is resulting in a marked anabolic response to teriparatide (TPTD) during the early phase after treatment initiation. Months later, due to coupling mechanism, the sustained increase of bone formation and ongoing anabolic effects are accompanied by significantly increased bone resorption as well. Antiresorptives influence the balance of bone formation and resorption. Therefore the investigators aim is to investigate the effects of the addition of antiresorptives to the second half of TPTD cycle when resorption is already also markedly elevated.