ADRB2 and chronic obstructive pulmonary disease: Inhaled β2-adrenergic receptor (β2AR) agonists remain the gold-standard for treatment of bronchoconstrictive pulmonary disorders such as asthma or chronic obstructive pulmonary disease (COPD), which are characterized by hypercontractility of smooth muscles that constrict airways leading to dyspnea, chest tightening, coughing and wheezing.