Inhaled corticosteroids contain a chemical that activates a cortisol receptor. Cortisol receptors are in many cells in the body, including the cells making the inflamed lining of the airways in patients with asthma and COPD. When the cortisol receptor is activated, the inflammatory response of the cells stops, and the lining of the airways returns to its original size. This allows better airflow and reduces the feelings of breathlessness in patients with COPD and asthma.
There are many inhaled corticosteroids sold in the US, the most common being fluticasone, which is sold as Flovent, budesonide, which is sold as Pulmicort, and mometasone, which is sold as Asmanex. They are long-acting medications, with a duration of action of roughly half a day. However they take multiple treatments before the medication reaches its full effectiveness. For this reason, inhaled steroids are not used as rescue inhalers. They are used primary for a long-term reduction of symptoms.
While systemic corticosteroids have significant side effects, especially after long-term use, very little of the inhaled steroids enters the bloodstream. Since they barely circulate systemically, inhaled steroids have far fewer side effects, even after long term use. One common side effect is the formation of thrush on the tongue and the rest of mouth. This is prevented by rinsing the mouth after every use.