A variable rate controlled delivery drive mechanism comprises: a drive mechanism housing, at least partially within which initially resides a biasing member positioned in an initially energized state within an inner cavity of a piston; a gear drive having a gear and a substantially axial internal pass-through; characterized in that it further comprises: a first screw which at least partially resides within the axial internal pass-through, said first screw also having a substantially axial pass-through and an external first pitch wherein the external first pitch is configured to engage a first nut which also resides within the internal pass-through of the gear drive; a second nut configured to engage a second screw having an external second pitch, said second nut positioned within an axial post of a piston, said axial post and second nut positioned to reside at least partially within the axial pass-through of the first screw; wherein the piston has an interface surface adjacent to a plunger seal 60 and is configured to axially translate the plunger seal, by force asserted upon it from the biasing member, from a first position to a second position within a drug container for drug delivery, and wherein the biasing member is metered from free expansion from its energized state. a drive mechanism housing, at least partially within which initially resides a biasing member positioned in an initially energized state within an inner cavity of a piston; a gear drive having a gear and a substantially axial internal pass-through; characterized in that it further comprises: a first screw which at least partially resides within the axial internal pass-through, said first screw also having a substantially axial pass-through and an external first pitch wherein the external first pitch is configured to engage a first nut which also resides within the internal pass-through of the gear drive; a second nut configured to engage a second screw having an external second pitch, said second nut positioned within an axial post of a piston, said axial post and second nut positioned to reside at least partially within the axial pass-through of the first screw; wherein the piston has an interface surface adjacent to a plunger seal 60 and is configured to axially translate the plunger seal, by force asserted upon it from the biasing member, from a first position to a second position within a drug container for drug delivery, and wherein the biasing member is metered from free expansion from its energized state. a first screw which at least partially resides within the axial internal pass-through, said first screw also having a substantially axial pass-through and an external first pitch wherein the external first pitch is configured to engage a first nut which also resides within the internal pass-through of the gear drive; a second nut configured to engage a second screw having an external second pitch, said second nut positioned within an axial post of a piston, said axial post and second nut positioned to reside at least partially within the axial pass-through of the first screw; wherein the piston has an interface surface adjacent to a plunger seal 60 and is configured to axially translate the plunger seal, by force asserted upon it from the biasing member, from a first position to a second position within a drug container for drug delivery, and wherein the biasing member is metered from free expansion from its energized state.