The present disclosure relates to an assisted injection device for injecting a composition contained in a medical container. The injection device includes a main body adapted to receive a medical container in a fixed position relative to the main body. The main body includes an inner wall part and a second part. The first part includes an inner spring-loaded piston rod, and an outer piston body extending coaxially around the inner spring-loaded piston rod. The second part is arranged between the inner spring-loaded piston rod and the outer piston body, and is provided of the piston. The actuator is adapted to selectively move the second part between the proximal first portion and the distal second position.
