According to one aspect of the present invention, an accessory for an aerosol inhalation system includes a main conduit body having an outlet end for placement close to a mouth of a patient, and first and second leg conduits that are in fluid communication with the main conduit body. The accessory further includes a holding chamber having a first compartment and a second compartment separated from the first compartment, with the first compartment being sealingly and fluidly coupled to the one port associated with the first leg conduit and the second compartment being sealingly and fluidly coupled to a port associated with the second leg conduit. An arrangement of valves is provided such that when the patient exhales, the first leg conduit is sealingly closed off from the main conduit body and the second leg conduit resulting in the aerosol particles flowing into and being held in the first compartment of the holding chamber. Conversely, when the patient inhales, the first leg conduit is opened to the main conduit body and in fluid communication with the second leg conduit resulting in the aerosol particles delivered through the first port being delivered to the patient.