An apparatus and method for transdermally delivering a biologically active agent comprising a delivery system having a microprojection member (or system) that includes a plurality of microprojections (or array thereof) that are adapted to pierce through the stratum corneum into the underlying epidermis layer, or epidermis and dermis layers. In one embodiment, the PTH-based agent is contained in a biocompatible coating that is applied to the microprojection member.