The drive mechanism for a drug delivery device comprises a lead screw (5) and a lead screw nut (7), which are aligned with an axis (4). The lead screw has screw threads (6, 16) having the same pitch and being intertwined. The lead screw nut has a drive feature which engages with the lead screw threads and guides a helical movement of the lead screw with respect to the lead screw nut during a dispense operation. The drive mechanism may comprise a drive member (9) which causes a helical movement of the lead screw via a coupling arrangement. The drive mechanism may further comprise stop features to inhibit helical movement of the lead screw when the drive member is moved in a non-dispensing direction. The drive mechanism provides an additional screw thread compared to common known drive mechanisms.
