A metered dose inhaler (MDI) spacer has a body that defines a dose receiving chamber. A proximal end portion coupled between the body and a mouth port through which a metered dose may be inhaled by a user of the MDI spacer. A distal end portion is coupled with the body. A combined one-way and flow rate control valve coupled with the distal end portion is configured for permitting external airflow into and prohibiting internal airflow out of the dose receiving chamber. A collar coupled with the distal end portion is configured for receiving an actuator shaft of a metered dose inhaler and for forming a seal about an aerosol nozzle of the metered dose inhaler such that a metered dose of medication is admissible into the dose receiving chamber via the collar while airflow into and out of the dose receiving chamber via the collar is prohibited.