A dispense mechanism for a drug delivery device for the delivery of a primary medicament in a primary cartridge and a secondary medicament in a secondary cartridge includes a primary drive member and a secondary drive member serve for driving a primary and a secondary lead screw. The primary drive member and the secondary drive member are configured to rotate during dose dispense. A coupling member serves for rotationally coupling the primary drive member to the secondary drive member and moves from a first position in which the primary drive member is rotationally decoupled from the secondary drive member into a second position in which the primary drive member is rotationally coupled to the secondary drive member during dose dispense. Rotation of the primary drive member moves the coupling member from the first position into the second position.