A dose adjustment mechanism for use with a resettable drug delivery device comprising: a drug delivery body (240； 404, 408； 516) that is an internal or external housing； a rotating sleeve (210； 406) in rotating coupling with respect to said housing； an actuator (230； 409； 530) releasably coupled to said rotating sleeve； and a spindle (242； 414； 542； 642) to drive a plug (218) of a cartridge (220), which spindle is operatively coupled to said actuator, such that when a user adjusts a dose by rotating said rotating sleeve , said actuator also rotates, wherein said spindle comprises a generally circular axis having an outer surface (560), said generally circular axis extending from a distal end to a proximal end of said circular axis； a first helical groove (219； 519； 619) provided along a first part of said outer surface (560) of said generally circular axis, said first helical groove having a first passage； and a second helical groove (221； 521； 621) provided along a second part of said outer surface (560) of said generally circular axis, said second helical groove (221； 521； 621) overlapping said first helical groove ( 219； 519； 619), said second helical groove having a second step； wherein the actuator (230； 409； 530) for driving said spindle comprises a helical grooved shape that engages with said first helical groove (219； 519； 619) of said spindle, and wherein the drug delivery body (404 , 408； 516) has a helical grooved shape that engages with said second helical groove (521； 621) of said spindle, wherein a longitudinal axial movement of the actuator causes the spindle to rotate characterized in that said actuator (230； 409) comprises a first tubular component (244； 412) and a second tubular component (246； 407), wherein one of said first and second components comprises at least one groove (296, 450) and the other of said first and second components comprises several recesses (300, 452) releasably connectable to the at least one groove (296, 450) with said firs
