A user-wearable infusion pump, comprising: a disposable cartridge including a reservoir configured to contain a medicament, the disposable cartridge including a plunger at a proximal end of the reservoir and an outlet port in fluid communication with the reservoir at a distal end of the reservoir; characterized in that the user-wearable infusion pump further comprises: a drive unit including at least one piezoelectric motor in contact with a drive disk, a threaded lead screw configured to rotate when drive disk is rotated, a pushrod, and a drive tube connected to the drive disk and wherein the lead screw is positioned within the pushrod and connected to the drive tube; wherein the drive unit is configured such that when the at least one piezoelectric motor is energized with an electrical drive signal, the at least one piezoelectric motor oscillates against the drive disk to cause the drive disk and the lead screw to rotate relative to the at least one piezoelectric motor around a common axis, wherein rotation of the drive disk causes rotation of the drive tube and the lead screw; and wherein each rotational movement of the drive disk in either direction about the common axis of rotation is configured to cause a corresponding rotational movement of the lead screw; wherein rotation of the lead screw causes linear motion of the pushrod relative to the at least one piezoelectric motor, and the linear motion of the pushrod moves the plunger to cause medicament to flow from the reservoir out of the outlet port to a patient without a gear reduction system. a disposable cartridge including a reservoir configured to contain a medicament, the disposable cartridge including a plunger at a proximal end of the reservoir and an outlet port in fluid communication with the reservoir at a distal end of the reservoir; characterized in that the user-wearable infusion pump further comprises: a drive unit including at least one piezoelectric motor in contact with a drive disk, a threaded lead screw configured to rotate when drive disk is rotated, a pushrod, and a drive tube connected to the drive disk and wherein the lead screw is positioned within the pushrod and connected to the drive tube; wherein the drive unit is configured such that when the at least one piezoelectric motor is energized with an electrical drive signal, the at least one piezoelectric motor oscillates against the drive disk to cause the drive disk and the lead screw to rotate relative to the at least one piezoelectric motor around a common axis, wherein rotation of the drive disk causes rotation of the drive tube and the lead screw; and wherein each rotational movement of the drive disk in either direction about the common axis of rotation is configured to cause a corresponding rotational movement of the lead screw; wherein rotation of the lead screw causes linear motion of the pushrod relative to the at least one piezoelectric motor, and the linear motion of the pushrod moves the plunger to cause medicament to flow from the reservoir out of the outlet port to a patient without a gear reduction system. a drive unit including at least one piezoelectric motor in contact with a drive disk, a threaded lead screw configured to rotate when drive disk is rotated, a pushrod, and a drive tube connected to the drive disk and wherein the lead screw is positioned within the pushrod and connected to the drive tube; wherein the drive unit is configured such that when the at least one piezoelectric motor is energized with an electrical drive signal, the at least one piezoelectric motor oscillates against the drive disk to cause the drive disk and the lead screw to rotate relative to the at least one piezoelectric motor around a common axis, wherein rotation of the drive disk causes rotation of the drive tube and the lead screw; and wherein each rotational movement of the drive disk in either direction about the common axis of rotation is configured to cause a corresponding rotational movement of the lead screw; wherein rotation of the lead screw causes linear motion of the pushrod relative to the at least one piezoelectric motor, and the linear motion of the pushrod moves the plunger to cause medicament to flow from the reservoir out of the outlet port to a patient without a gear reduction system.