A metered-dose inhaler delivers topical medications to the respiratory tract, producing local and systemic effects. The mucosal lining of the respiratory tract absorbs the inhalant almost immediately. Examples of common inhalants include bronchodilators, which improve airway patency and facilitate mucous drainage; mucolytics, which attain a high local concentration to liquefy tenacious bronchial secretions; and corticosteroids, which decrease inflammation.

The use of these inhalers may be contraindicated in patients who can’t form an airtight seal around the device and in patients who lack the coordination or clear vision to assemble the inhaler. Some patients use a spacer to assist them with the airtight seal. Specific inhalants may also be contraindicated. For example, bronchodilators are contraindicated if the patient has tachycardia or a history of cardiac arrhythmias associated with tachycardia.