A medication injection pen comprises a dose set knob rotatable with respect to a housing to set a desired injection dose. The dose set knob comprises at least one internal thread. A leadscrew includes a thread element for advancing in a first direction via a corresponding thread engagement. A driver is rotationally fixed to the leadscrew and is rotatable in a first direction to rotate and advance the leadscrew in the first direction. The setback member is rotationally fixed to the driver. The dose stop member is rotationally coupled to the setback member and is axially movable relative to the dose set knob when the dose set knob is rotated relative to the setback member. Axial movement of the dose stop member limits the user from setting a dose that is greater than an injectable volume of medication remaining in a cartridge.