Symbicort Inhaler 160/4.5 mcg contains Formoterol 4.5mcg and Budesonide 160mcg used in the treatment of asthma and chronic obstructive pulmonary disease. Formoterol is a long-acting bronchodilator which works by relaxing the muscles in the airways and widens the airways. Budesonide is a steroid. It works by stopping the release of certain chemical messengers that cause inflammation (swelling) of the airways. Together they make breathing easier.