Abstract: The present invention relates to a single-use syringe comprising a barrel (10) having an internal surface defining a chamber for retaining a fluid, a plunger (1) formed by an elongated body including a plurality of longitudinal fins (2) and optionally a piston (3) connected to the end of the plunger close to the needle, the external surface of the piston or of the end of the plunger in the case of not including a piston being in leak-tight connection with the internal surface of the barrel, where the barrel has a general external shape of a cylinder of revolution with a constant radius circular base and a variable internal shape, forming the wall of the barrel with variable thickness, generating a chamber inside which a plunger incorporating a plurality of fins (2) slides; each of the longitudinal fins (2) of the plunger has a constant height along its entire length but different from that of at least one of the other fins, which height is suitable in each fin so that the plunger (1) can be inserted tightly w