The methacholine challenge test is used to assess the abnormal airway function in the bronchi by introducing the drug (methacholine) which causes contraction of smooth muscle and airway obstruction. From this comes the term methacholine challenge test, because it attempts to observe the reaction that produces this drug applied in increasing doses. This test is performed by spirometry before, during and after administration of inhaled methacholine. It takes about an hour, and during this time the symptoms presented by the patient are recorded. These tend to be mild and short-lived, such as cough, shortness of breath, coughing, headache, etc.