A patient controlled liquid drug administration device, comprising: an elongated housing having an axial cavity extending through it; a reciprocating pump mounted at a bottom end of the cavity, the pump defining a closed reservoir and having a first wall fixed in the cavity and a second wall axially movable therein with respect to the first wall between reservoir-full and reservoir-empty positions; an inlet conduit having a first end connected to an inlet port of the pump and an opposite second end connectable to a source of pressurized liquid drug; an outlet conduit having a first end connected to an outlet port of the pump and an opposite second end subcutaneously connectable to the patient; an elongated plunger captivated in the cavity above the pump for axial movement between raised and lowered positions and having a lower end contacting the movable wall of the pump; an elongated button captivated in the cavity above the plunger for axial movement between extended and depressed positions; and a compression spring axially disposed between the plunger and the button; and characterised by comprising: a clamp mounted in the cavity to move between a closed position constricting the outlet conduit and thereby preventing the flow of liquid through it, and an open position disengaged from the outlet conduit, thereby allowing the flow of liquid through it; a spring biasing the clamp toward its closed position; wherein; the button has a detent for latching the button in the depressed position, and a ledge that engages the clamp and moves it to its open position when the button is moved to its depressed position; and further comprising: a spring catch mounted in the cavity that resiliently engages the detent in the button when the button is moved to its depressed position and holds the button in its depressed position against an upward urging of the compression spring; and, a catch release on the plunger that disengages the spring catch from the detent in the button when the plunger is moved to its lowered position. an elongated housing having an axial cavity extending through it; a reciprocating pump mounted at a bottom end of the cavity, the pump defining a closed reservoir and having a first wall fixed in the cavity and a second wall axially movable therein with respect to the first wall between reservoir-full and reservoir-empty positions; an inlet conduit having a first end connected to an inlet port of the pump and an opposite second end connectable to a source of pressurized liquid drug; an outlet conduit having a first end connected to an outlet port of the pump and an opposite second end subcutaneously connectable to the patient; an elongated plunger captivated in the cavity above the pump for axial movement between raised and lowered positions and having a lower end contacting the movable wall of the pump; an elongated button captivated in the cavity above the plunger for axial movement between extended and depressed positions; and a compression spring axially disposed between the plunger and the button; and characterised by comprising: a clamp mounted in the cavity to move between a closed position constricting the outlet conduit and thereby preventing the flow of liquid through it, and an open position disengaged from the outlet conduit, thereby allowing the flow of liquid through it; a spring biasing the clamp toward its closed position; wherein; the button has a detent for latching the button in the depressed position, and a ledge that engages the clamp and moves it to its open position when the button is moved to its depressed position; and further comprising: a spring catch mounted in the cavity that resiliently engages the detent in the button when the button is moved to its depressed position and holds the button in its depressed position against an upward urging of the compression spring; and, a catch release on the plunger that disengages the spring catch from the detent in the button when the plunger is moved to its lowered position. a clamp mounted in the cavity to move between a closed position constricting the outlet conduit and thereby preventing the flow of liquid through it, and an open position disengaged from the outlet conduit, thereby allowing the flow of liquid through it; a spring biasing the clamp toward its closed position; wherein; the button has a detent for latching the button in the depressed position, and a ledge that engages the clamp and moves it to its open position when the button is moved to its depressed position; and further comprising: a spring catch mounted in the cavity that resiliently engages the detent in the button when the button is moved to its depressed position and holds the button in its depressed position against an upward urging of the compression spring; and, a catch release on the plunger that disengages the spring catch from the detent in the button when the plunger is moved to its lowered position. a spring catch mounted in the cavity that resiliently engages the detent in the button when the button is moved to its depressed position and holds the button in its depressed position against an upward urging of the compression spring; and, a catch release on the plunger that disengages the spring catch from the detent in the button when the plunger is moved to its lowered position.