The injector has a housing part (1), piston body (2) and a locking cap (3) with a cap part for locking an opening of the injector and with a connection part for connecting the locking cap with the injector. The cap part and the connection part are detachably connected through a tearing edge. The housing part is provided with an undercut, and the piston body is provided with a projection, where the undercut and the projection are co-ordinated. The piston body is single-piece formed, where the piston body has a slide and a piston.
