A drug delivery device has a housing with an adhesive pad associated with the lower surface of the housing and configured to removably attach to a human body surface. A drug reservoir is positioned within the housing and includes an outlet with a valve, with a needle fluidically connected to the reservoir and configured to define at least a portion of a fluid flow path between the reservoir and the human body surface. A controller is configured to control the components of the drug delivery device to execute a drug delivery routine. The drug delivery device also includes pressurized fluid positioned to apply a force to the reservoir. The controller moves the valve from a closed condition to an open condition during a drug delivery routine to allow the pressurized fluid to deform the reservoir or move a plunger to convey the drug out of the reservoir via the outlet.