A gas therapy system (1) has a flow line (3, 2), a coupler (6) to a gas source, and an aerosol generator (4) for aerosol delivery, and a patient interface such as a nasal interface (2). A controller (10) is configured to modulate gas flow and aerosol delivery in real time. The controller changes gas flow rate and dynamically reduces aerosol delivery during upper gas flow rates such as 60 LPM, and activates aerosol delivery during lower gas flow rates of for example 10 LPM. The control may also include sensors to detect breathing, so that there is a bias towards increased aerosol delivery during inhalation in addition to during lower level gas flow.