Disposable injector with a housing, in which or on which - respectively at least in certain areas - at least one mechanical spring-energy storage, at least one cylinder-piston unit which can be filled at least occasionally with active ingredient, at least one piston-actuating plunger and at least one actuating unit are arranged, - whereby the spring-energy storage includes at least one pre-stressed spring-loaded element and - whereby at least part of the piston-actuating plunger is positioned between the spring-energy storage and a piston of the cylinder-piston unit, - whereby the housing has at least one draw hook, - whereby the individual draw hook has at least one support surface respectively in the region of its free end, - whereby the spring-loaded piston-actuating plunger rests on the support surface against a position which prevents any actuation of the disposable injector, - whereby the contact zone placed between the draw hook and the piston-actuating plunger represents a variable-speed gear pair thrusting the draw hook radially outwards, - whereby the locking position of the draw hook is secured by an actuating element positioned in a locked position, and - whereby the actuating element has a triggering position which effects radially outwards aligned retreat of the draw hook when the piston-actuating plunger is released, characterized in that - the draw hook or the draw hooks is/are formed at least in certain areas as flexural elastic-outward-springing-elements on the housing, which elements represent a flexional beam, - the release element has at its upper end a flange-like, outwardly protruding collar to which an actuating cap is attached, which fully encloses the rear end of the housing with clearance, and - the actuating cap has a widened region which is configured such that, when the release sleeve is pushed down into the triggering position in the direction of the cylinder-piston unit, the flexional beams slip outwards into the widened region and are taken up in the widened region. - whereby the spring-energy storage includes at least one pre-stressed spring-loaded element and - whereby at least part of the piston-actuating plunger is positioned between the spring-energy storage and a piston of the cylinder-piston unit, - whereby the housing has at least one draw hook, - whereby the individual draw hook has at least one support surface respectively in the region of its free end, - whereby the spring-loaded piston-actuating plunger rests on the support surface against a position which prevents any actuation of the disposable injector, - whereby the contact zone placed between the draw hook and the piston-actuating plunger represents a variable-speed gear pair thrusting the draw hook radially outwards, - whereby the locking position of the draw hook is secured by an actuating element positioned in a locked position, and - whereby the actuating element has a triggering position which effects radially outwards aligned retreat of the draw hook when the piston-actuating plunger is released, - the draw hook or the draw hooks is/are formed at least in certain areas as flexural elastic-outward-springing-elements on the housing, which elements represent a flexional beam, - the release element has at its upper end a flange-like, outwardly protruding collar to which an actuating cap is attached, which fully encloses the rear end of the housing with clearance, and - the actuating cap has a widened region which is configured such that, when the release sleeve is pushed down into the triggering position in the direction of the cylinder-piston unit, the flexional beams slip outwards into the widened region and are taken up in the widened region.