Clenbuterol is a sympathomimetic β2-adrenoceptor agonist that has been used as a bronchodilator (20 μg per dose in humans) in the treatment of pulmonary diseases such as asthma. At higher doses (2 mg/kg/day in rats), clenbuterol acts as an anabolic steroid, favoring skeletal muscle protein synthesis at the expense of fat deposition. Because of this property, clenbuterol has been illegally used by athletes to enhance performance, by dieters to encourage weight loss, and by livestock farmers to produce animals with leaner meat. The use of clenbuterol is banned by the U.S. Food and Drug Administration as well as the International Olympic Committee and is prohibited for use in food-producing animals in the U.S., the European Union, and China. Clenbuterol can also produce relaxation of smooth muscle in the uterus and has been used in the short-term postponement of parturition in veterinary obstetrical procedures.
