A drive assembly for a drug delivery device is disclosed. The drive assembly is connectable with a cartridge holder and comprises a housing, a piston rod, the piston rod being movable in a distal direction for drug delivery, and a guide nut, the guide nut being rotatable relative to the housing around an axis of the assembly and provided for guiding the piston rod. A locking means is provided which is enabled to take an engaged state in which the locking means is engaged with the guide nut in order to prevent rotation of the guide nut and to take a disengaged state in which the locking means is disengaged from the guide nut in order to allow rotation of the guide nut. Moreover, a coupling means is provided, the coupling means being rotatable relative to the housing around the axis of the assembly for interaction with the locking means in order to change between the engaged state and the disengaged state of the locking means.