An assembly includes a cartridge containing doses of a drug and a piston rod adapted and arranged to expel drug from the cartridge, the piston rod including a thread. The assembly further includes a nut member adapted and arranged to be rotated with respect to the piston rod about a rotational axis. The assembly further comprises a last dose stop mechanism adapted including at least one first interaction member and at least one second interaction member provided by the piston rod and at least one first stop member and at least one second stop member provided by the nut member. The interaction members and the stop members are configured to mechanically cooperate with one another such that further relative movement of the nut member and the piston rod for setting a dose of the drug is prevented.
