The invention relates to a dose setting mechanism (4), which is operable to be coupled to a medication cartridge (25) and which comprises means that prevent the user from setting a dose greater than the remaining medication in the cartridge (25). The dose setting mechanism comprises a shaft (30). A helical groove (32) having a first pitch is provided along a first portion (32) of the shaft (30). The dose setting mechanism (4) further comprises a nut member (40) disposed on the helical groove (32) of said shaft (30). During dose setting, the shaft (30) is rotated relative to the nut member (40) while the nut member (40) traverses along the groove (32) from a distal end (38) of the shaft (30) towards a proximal end (39) of the shaft (30). The mechanism further comprises means preventing a user of said dose setting mechanism (4) from setting a dose of said medication that is greater than said remaining medication in said cartridge (25), said means comprising a second pitch provided along a second portion (36) of said shaft (30), wherein said first pitch is different from said second pitch, wherein said second pitch is preferably greater than said first pitch.L’invention concerne un mécanisme doseur (4) conçu pour saccoupler à une cartouche à médicament (25) et comprenant un moyen qui empêche lusager de fixer une dose supérieure à la quantité de médicament restant dans la cartouche (25). Le mécanisme doseur (4) comprend un axe (30). Une rainure hélicoïdale (32) présentant un premier pas est creusée le long dune première partie (32) de laxe (30). Le mécanisme doseur (4) comprend également un élément écrou (40) disposé sur la rainure hélicoïdale (32) dudit axe (30). Lors du réglage de la dose, laxe (30) entre en rotation relativement à lélément écrou (40) pendant que ce dernier (40) accomplit sa course le long de la rainure (32), dune extrémité distale (38) à une extrémité proximale (39) de laxe (30). Le mécanisme doseur (4) comprend en outre un moyen qui empêche son usag
