A patch injector for parenteral administration of a drug to a drug recipient having a skin surface, the patch injector comprising: a drug-cartridge module having a drug reservoir with a longitudinal drug-reservoir axis; a plunger movably disposed in the drug reservoir; a power-pack module attached to the proximal end of the drug-cartridge module; a compressed, elastic power element disposed in the power-pack module and coupled to the plunger, the compressed, elastic power element expandable along the drug-reservoir axis; a drug-recipient interface module connected to the power-pack module, the drug-recipient interface module comprising: a skin-contact surface extending parallel to the drug-reservoir axis; an injection-needle insertion mechanism driven by the compressed, elastic power element and wherein the injection-needle insertion mechanism comprises an insertion-mechanism frame on which the drug-cartridge module and the power-pack module are mounted, and the insertion-mechanism frame is pivotably coupled to the skin-contact surface by a pivot offset from the drug-reservoir axis; an injection needle disposed at the distal end of the injection-needle insertion mechanism, the injection needle in fluid communication with die drug reservoir and oriented orthogonal to the drug reservoir and generally toward the skin-contact surface, characterized in that, the compressed, elastic power element is configured to displace the plunger distally into the drug reservoir and to move the injection needle toward the skin-contact surface when the compressed, elastic power element expands distally along the drug-reservoir axis generating a bending moment in the injection-needle insertion mechanism, wherein the proximal end of the compressed, elastic power element disposed in the power-pack module is fixedly attached to an extension of the skin-contact surface and expansion of the compressed, elastic power element generates a bending moment that rotates the insertion-mechanism frame driving the injection needle toward the skin-contact surface. a drug-cartridge module having a drug reservoir with a longitudinal drug-reservoir axis; a plunger movably disposed in the drug reservoir; a power-pack module attached to the proximal end of the drug-cartridge module; a compressed, elastic power element disposed in the power-pack module and coupled to the plunger, the compressed, elastic power element expandable along the drug-reservoir axis; a drug-recipient interface module connected to the power-pack module, the drug-recipient interface module comprising: a skin-contact surface extending parallel to the drug-reservoir axis; an injection-needle insertion mechanism driven by the compressed, elastic power element and wherein the injection-needle insertion mechanism comprises an insertion-mechanism frame on which the drug-cartridge module and the power-pack module are mounted, and the insertion-mechanism frame is pivotably coupled to the skin-contact surface by a pivot offset from the drug-reservoir axis; an injection needle disposed at the distal end of the injection-needle insertion mechanism, the injection needle in fluid communication with die drug reservoir and oriented orthogonal to the drug reservoir and generally toward the skin-contact surface, a skin-contact surface extending parallel to the drug-reservoir axis; an injection-needle insertion mechanism driven by the compressed, elastic power element and wherein the injection-needle insertion mechanism comprises an insertion-mechanism frame on which the drug-cartridge module and the power-pack module are mounted, and the insertion-mechanism frame is pivotably coupled to the skin-contact surface by a pivot offset from the drug-reservoir axis; an injection needle disposed at the distal end of the injection-needle insertion mechanism, the injection needle in fluid communication with die drug reservoir and oriented orthogonal to the drug reservoir and generally toward the skin-contact surface, characterized in that, the compressed, elastic power element is configured to displace the plunger distally into the drug reservoir and to move the injection needle toward the skin-contact surface when the compressed, elastic power element expands distally along the drug-reservoir axis generating a bending moment in the injection-needle insertion mechanism, wherein the proximal end of the compressed, elastic power element disposed in the power-pack module is fixedly attached to an extension of the skin-contact surface and expansion of the compressed, elastic power element generates a bending moment that rotates the insertion-mechanism frame driving the injection needle toward the skin-contact surface.