An assembly for a drug delivery device (1) is provided, the assembly comprising a piston rod (10) and a force transfer subassembly (16, 17), the force transfer subassembly being arranged and configured, in a driving mode of operation of the assembly, to transfer a driving force (F) to the piston rod in order to drive the piston rod, the force transfer subassembly comprising a first force transfer member (17), and a second force transfer member (16), wherein the first force transfer member and the second force transfer member are operatively coupled to each other via a force-sensitive coupling (27) to transfer the driving force to the piston rod, and wherein, when an excessive force acts on the force-sensitive coupling, the force-sensitive coupling is arranged and configured to be released in order to switch the assembly from the driving mode of operation into a security mode of operation.
