A medication injection pen is provided comprising a housing (218), for housing a dose set knob (220), a leadscrew (226), a driver (224), a setback member (222), and a dose stop member (228). The dose set knob (220) is rotatable with respect to said housing (218) to set a desired injection dose, and comprises at least one internal thread (291). The leadscrew (226) includes a thread element by which it is advanceable in a first direction via a corresponding thread engagement, said first direction being that which expels medication from a cartridge (36). The driver (224) is rotationally fixed to said leadscrew (226) for preventing relative rotation therebetween, said driver (224) being rotatable in a first direction to rotate and advance said leadscrew (226) in said first direction. The setback member (222) is rotationally fixed to said driver (224) for preventing relative rotation therebetween.
