A drug mixing device is disclosed. The drug mixing device comprises a container for containing a fluid component of a drug to be mixed and a housing. The housing comprises an inlet aperture configured to be connected to a fluid driver for driving a driving fluid into the container and an outlet aperture configured to permit the fluid component of the drug to be mixed to leave the container. The apertures are arranged such that the driving fluid enters the container through the inlet aperture, and additionally arranged such that the fluid component exits the container through the outlet aperture, the driving fluid having a lower density than the fluid component. The inlet aperture and the outlet aperture are arranged such that, in use, the inlet aperture is located above the outlet aperture.
