A handheld injection device (10) comprising an needle cannula, a reservoir configured for containing a liquid drug to be dispensed, a piston, a trigger button (22), an elongated, hollow outer housing (20) in which the reservoir is positioned, the needle cannula being in liquid communication with the reservoir and extending from one end of the housing, wherein the injection device further comprises a drive mechanism comprising a spring or a resilient member, the spring or a resilient member being configured to provide a driving force when the trigger button is pressed allowing the piston to be advanced by the drive mechanism thus causing a dose of the liquid drug to be dispensed, wherein the handheld injection device comprises a variable friction system being adapted to apply a variable counter force leveling out the driving force.
