An autoinjector comprising: a spring holder; a guide cylinder releasably coupled to the spring holder, the guide cylinder adapted to accommodate a syringe including an inner plunger, wherein a distal end of the inner plunger is coupled to a stopper; a drive spring; a rear case adapted to engage the spring holder; characterized in a drive assembly releasably coupled to the spring holder, the drive assembly coupled to the guide cylinder; wherein the drive spring is adapted to apply a force on the drive assembly; wherein the syringe includes a needle retraction mechanism including the inner plunger telescopically coupled to an outer plunger, wherein a plunger spring biases the outer plunger relative to the inner plunger, wherein a resilient arm (9.1) on the inner plunger engages the inner plunger to the outer plunger, wherein a release ring on a finger flange of the syringe is adapted to engage the resilient arm (9.1), causing the arm (9.1) to deflect and disengage the outer plunger, wherein when the arm (9.1) disengages the outer plunger, the plunger spring expands, and the inner plunger can move axially relative to the outer plunger; wherein the drive spring is wrapped over the guide cylinder, wherein a distal end of the drive spring is grounded in a recess in the rear case while a proximal end of the drive spring is grounded in the drive assembly which is also wrapped over the guide cylinder, wherein, in use, the drive assembly is adapted to engage the outer plunger and moves in a distal direction relative to the guide cylinder; and a penetration spring adapted to apply a force on the guide cylinder. a spring holder; a guide cylinder releasably coupled to the spring holder, the guide cylinder adapted to accommodate a syringe including an inner plunger, wherein a distal end of the inner plunger is coupled to a stopper; a drive spring; a rear case adapted to engage the spring holder; characterized in a drive assembly releasably coupled to the spring holder, the drive assembly coupled to the guide cylinder; wherein the drive spring is adapted to apply a force on the drive assembly; wherein the syringe includes a needle retraction mechanism including the inner plunger telescopically coupled to an outer plunger, wherein a plunger spring biases the outer plunger relative to the inner plunger, wherein a resilient arm (9.1) on the inner plunger engages the inner plunger to the outer plunger, wherein a release ring on a finger flange of the syringe is adapted to engage the resilient arm (9.1), causing the arm (9.1) to deflect and disengage the outer plunger, wherein when the arm (9.1) disengages the outer plunger, the plunger spring expands, and the inner plunger can move axially relative to the outer plunger; wherein the drive spring is wrapped over the guide cylinder, wherein a distal end of the drive spring is grounded in a recess in the rear case while a proximal end of the drive spring is grounded in the drive assembly which is also wrapped over the guide cylinder, wherein, in use, the drive assembly is adapted to engage the outer plunger and moves in a distal direction relative to the guide cylinder; and a penetration spring adapted to apply a force on the guide cylinder.