Systems and methods are provided for delivering one or more drugs. In some embodiments, a drug delivery system includes a housing having a distal end with an inlet through which an inspiratory flow of air passes into the housing, a proximal end having a patient interface attached thereto, the patient interface being configured to interface with a user, and an inspiratory flow pathway extending from the distal end to the proximal end of the housing. A nitric oxide (NO) source is positioned within the housing and is configured to deliver NO-containing gas to the patient interface. A secondary drug source is positioned within the housing and is configured to deliver a secondary drug to the patient interface. A controller is configured to control an amount of NO-containing gas and an amount of the secondary drug delivered using a control scheme.