Budesonide is used to control and prevent symptoms (wheezing and shortness of breath) caused by asthma. This medication belongs to a class of drugs known as corticosteroids. It works directly in the lungs to make breathing easier by reducing the irritation and swelling of the airways. This medication must be used regularly to be effective. It does not work right away and should not be used to relieve sudden asthma attacks. If an asthma attack occurs, use your quick-relief inhaler as prescribed.