A medical injection device (10, 20, 30, 40, 50) having a distal end and a proximal end, comprising: a medication container (111, 112, 209, 509) having a movable piston (111e, 112b, 209a, 509a); a cylinder (102, 202, 302, 402) at said proximal end of said medical injection device and a cylinder (103, 203, 303, 403, 503) at said distal end of said medical injection device; a push rod assembly displaceably disposed in said medical injection device, said push rod assembly having a plurality of spaced-apart position setting means disposed along the length thereof, said push rod assembly selectively displacing said movable piston (111e, 112b, 209a, 509a) to dispense a medicament from said medication container (111, 112, 209, 509); a first resilient member (106, 206, 306, 406, 506) configured to bias said push rod assembly to move toward said distal end of said medical injection device; a releasable restraining means (107a, 204a, 307a, 407a, 507a) configured to releasably restrain said push rod assembly in a locked state against said biasing of said first resilient member (106, 206, 306, 406, 506), wherein, upon release of said releasable restraining means (107a, 204a, 307a, 407a, 507a), said push rod assembly moves under force of said first resilient member (106, 206, 306, 406, 506) toward said distal end of said medical injection device; a push cap (101, 201, 301, 401) configured to release said releasable restraining means (107a, 204a, 307a, 407a, 507a); and characterized by an arming means comprising a second resilient member (105, 205, 305, 405, 505) configured to move said push rod assembly toward said proximal end of said medical injection device. a medication container (111, 112, 209, 509) having a movable piston (111e, 112b, 209a, 509a); a cylinder (102, 202, 302, 402) at said proximal end of said medical injection device and a cylinder (103, 203, 303, 403, 503) at said distal end of said medical injection device; a push rod assembly displaceably disposed in said medical injection device, said push rod assembly having a plurality of spaced-apart position setting means disposed along the length thereof, said push rod assembly selectively displacing said movable piston (111e, 112b, 209a, 509a) to dispense a medicament from said medication container (111, 112, 209, 509); a first resilient member (106, 206, 306, 406, 506) configured to bias said push rod assembly to move toward said distal end of said medical injection device; a releasable restraining means (107a, 204a, 307a, 407a, 507a) configured to releasably restrain said push rod assembly in a locked state against said biasing of said first resilient member (106, 206, 306, 406, 506), wherein, upon release of said releasable restraining means (107a, 204a, 307a, 407a, 507a), said push rod assembly moves under force of said first resilient member (106, 206, 306, 406, 506) toward said distal end of said medical injection device; a push cap (101, 201, 301, 401) configured to release said releasable restraining means (107a, 204a, 307a, 407a, 507a); and characterized by an arming means comprising a second resilient member (105, 205, 305, 405, 505) configured to move said push rod assembly toward said proximal end of said medical injection device.