The present disclosure relates to a stopper configured to be positioned inside a barrel of an injection device for injecting at least one composition, said stopper including: a gasket including a proximal end, a distal end, a lateral wall, and a through hole extending from the proximal end to the distal end, an insert inserted in the through hole, wherein the stopper is adapted to deform between: a closed configuration wherein the gasket cooperates with the insert to hermetically close the through hole, for preventing flow of the composition between the proximal end and the distal end of the gasket, and an open configuration wherein the gasket cooperates with the insert to open a fluidic pathway in the through hole between the proximal end and the distal end of the gasket for allowing flow of the composition.