A syringe comprising: a body delimiting a chamber； a piston able to slide in the chamber of the body along a longitudinal axis of the syringe, wherein the piston comprises a rod, a head, and a finger rest, which are all in one piece； and a deformable retention device designed to prevent the piston from leaving the body entirely, wherein the retention device is force-fitted in the chamber, extends around the piston over an angular sector strictly greater than 180° when it is in the assembled position, and has protruding external ribs which extend parallel to the longitudinal axis and are plastically deformable when the retention device is assembled in the chamber.
