Inhalers deliver oral medication to the respiratory system, and they are commonly used to treat asthma, Mayo Clinic states. Metered-dose inhalers contain a pressurized gas in a canister, which is attached to a mouthpiece, and the canister releases the correct amount of medication when pressed.
In some cases, asthmatics need a spacer to consume the complete dosage in a metered-dose inhaler, according to Mayo Clinic. A spacer is a long tube that fits on the mouthpiece, which slows down the speed at which the inhalant travels, giving the individual more time to breath in the medication. When using dry powder inhalers, users must breathe quickly and deeply to inhale powder from a dispensing tube.