Manipulation of respiratory physiology by pharmacological intervention is a significant role of the anaesthetist and intensivist. Successful use of these various agents requires a thorough understanding of their mechanisms of actions, potential side effects and limitations. These interventions involve changes in airway calibre, secretions and sensitivity of the airway to noxious stimuli. Other agents act to inhibit the depressant effect that sedatives may have on the patient's respiratory drive. The effects, both advantageous and detrimental, may be complicated by the action of other disease processes which affect the metabolism of these drugs. There are multiple possible routes of administration which allows flexibility for the clinician and may reduce systemic effects, thereby limiting side effect profiles. Drugs used specifically in the treatment of acute respiratory distress syndrome attempt to alter pulmonary ventilation and perfusion thereby reduce mismatching and improve diffusion capacity.