A syringe assembly is disclosed comprising a barrel 12 for containing one or more medicaments and a stopper 14 disposed in the barrel 12. The stopper 14 defines and separates a first volume 24 and a second volume 26 within the syringe assembly. The stopper 14 comprises a permanent seal 16 fluidly sealing the stopper 14 to the barrel 12 about the entire perimeter of the stopper 14. A channel 18 is located in the stopper 14 and bypasses the permanent seal 16. The first opening 20a of the channel 18 is in fluid communication with the second volume 26 and the second opening 20b is selectively sealed from the first volume 24 by a resilient seal 22. The resilient seal 22 is moveable between a sealing configuration, where it seals the stopper 14 to the barrel 12 to prevent the first volume 24 entering the channel 18, and an open configuration where the first volume 24 can enter the channel 18. The resilient seal 22 changes configuration when the fluid pressure in the first volume or second volume exceeds a pressure threshold.
