Abstract: Hypodermic syringe with a blockable piston capable of preventing it recharge and reuse, comprising a cylindrical tubular body having a communicating container in its inlet end; a right-angled section piston rod; a first blocking means constituted by at least one member placed in abutment against rotation over the container bottom and opposed alternatively to on and the other of toothed intermediate sections of the piston rod; and a second blocking means slidingly mounted over the piston rod, placed in abutment with the first blocking means and urged in positional fastening by an elastic retention member constituting in turn, the lid of the container.