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 (D) 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 (D) relative to the guide cylinder ; and a penetration spring adapted to apply a force on the guide cylinder . <EOS>