Automatic drug delivery device

In one aspect, the invention provides a drug delivery device comprising a drug container assembly (16) and a plunger (18) positioned within the drug container assembly. The drug container assembly includes: an outlet for dispensing medicament, wherein the outlet is sealed at an initial position; a driving mechanism comprising a first stored energy source (42) and being operable to apply pressure to the plunger or the drug container to pressurize the medicament; and the first release mechanism that is operable to unseal the outlet after the medicament has been pressurized. In another aspect, a drug delivery device is provided with: a housing comprising an outer housing portion configured to be held in use and a drug containing portion containing a drug; a needle assembly comprising a needle secured to a needle hub, where the needle hub is configured to move relative to the drug containing portion from an initial position within the housing to an inserted position in which the needle extends beyond the housing;