A droplet delivery device and related methods for delivering precise and repeatable dosages to a subject for pulmonary use is disclosed. The droplet delivery device includes a housing, a reservoir, and ejector mechanism, and at least one differential pressure sensor. The droplet delivery device is automatically breath actuated by the user when the differential pressure sensor senses a predetermined pressure change within housing. The droplet delivery device is then actuated to generate a stream of droplets having an average ejected droplet diameter within the respirable size range, e.g, less than about 5 µm, so as to target the pulmonary system of the user.