A nasal droplet delivery device and related methods for delivering precise and repeatable dosages to a subject via the nasal passageways and sinus cavities is disclosed. The droplet delivery device includes a housing, a nosepiece, a reservoir, an ejector mechanism, and at least one differential pressure sensor. The droplet delivery device is automatically actuated by the user when the differential pressure sensor senses a predetermined pressure change within the nosepiece. The droplet delivery device is then actuated to generate a plume of droplets having an average ejected particle diameter of greater than about 6 microns, preferably greater than about 10 micron, so as to target the nasal passageways and sinus cavities of the user.