According to one aspect of the present invention, an aerosol inhalation system includes a first conduit member for delivering medication in the form of aerosol particles to a patient. The system also includes a first device in fluid communication with the first holding chamber for producing the aerosol particles and being sealingly yet releasably received within an adapter that forms an entrance into a first holding chamber. The adapter has a compressible material disposed thereon which is at least partially compressed by insertion of the first device to form the seal between the first device and the adapter, thereby creating a closed system that is therefore capable of delivering a fixed concentration of the medication to the patient due to a valve of the valve mechanism being closed when the patient inhales and the medication is delivered to the patient.