A dose setting mechanism that prevents dispensing of a drug when an incorrect cartridge assembly is attached to the dose setting mechanism. Dispense of a drug may be allowed by preventing rotation of a spindle nut of a drug delivery device, and dispense of a drug may be prevented by not preventing rotation of the spindle nut. Preventing dispense of a drug may be accomplished by preventing rotation of the spindle when an incorrect cartridge assembly is inserted. Preventing dispense of a drug may be accomplished by preventing the spindle from applying an axial force on the cartridge when an incorrect cartridge assembly is inserted.
