The present invention provides a minimally invasive, disposable, self- powered, patch-like drug delivery device. The device generally comprises a microneedle; a drug reservoir in fluid communication with the microneedle and comprising a drug to be administered; a pressure chamber in gas communication with the drug reservoir and comprising a liquid medium; a trigger for initiating a chemical reaction in the pressure chamber; and a plunger disposed in the drug reservoir, adapted to move unidirectionally in response to a pressure increase in the pressure chamber and to insulate the drug in the drug reservoir from a reactant and/or a product of the chemical reaction. Kits and methods for using the device are also provided.