A medication injection pen, including a housing, a dose set knob (DSK) comprising an internal thread and an internal key proximate to a distal end of the internal thread, and a dose stop member comprising an external thread engaging the internal thread of the dose set knob. Rotation of the dose set knob to set a medication dose causes lateral translation of the dose stop member with respect to the dose set knob, and when the dose set knob is rotated to a last dose setting position, the dose stop member rotationally abuts the internal key thereby preventing further rotational movement of the dose set knob in a dose setting direction.