A disposable injector with a piston actuation ram is mounted in a housing, is loaded by a spring energy accumulator and can be unlocked by a displaceable trigger device. The piston actuation ram can be supported by a tensioning rod mounted in the housing. The trigger device comprises a trigger ring displaceable relative to the housing. The tensioning rod can be supported directly or indirectly by a bearing surface of the trigger ring. The bearing surface encloses an angle of between ten degrees and forty five degrees with the longitudinal direction of the disposable injector. The point of the angle lies offset with respect to the trigger ring in the triggering direction of the disposable injector. A disposable injector with increased trigger reliability is developed.