The United States Food and Drug Administration approved the clenbuterol-based Ventipulmin Syrup, produced by Boehringer Ingelheim Vetmedica, Inc., as a prescription-only drug for the treatment of airway obstruction in horses (0.8-3.2 m g/kg twice daily) in 1998. Clenbuterol is not meant for human use or for use in food-producing animals. As of fall, 2006, clenbuterol is not an ingredient of any therapeutic drug approved by the U.S. FDA.

But, outside the U.S., clenbuterol is often used as prescription drug for the treatment of bronchial asthma in humans. It is used as a powerful, long-lasting bronchodilator and tocolytic in many countries of the world. It is available in tablets (0.01 or 0.02 mg per tablet) and liquid preparations.

However, clenbuterol is widely and generally used by bodybuilders and athletes for its ability to increase lean muscle mass and reduce body fat (i.e., repartitioning effects). It is commonly used for smooth muscle relaxant properties. It is often used for its ability to alter body composition by reducing body fat and increasing skeletal muscle mass. It is usually often used in combination with other performance enhancing drugs, such as anabolic steroids and growth hormone. However, clenbuterol is usually linked with significant adverse cardiovascular and neurological effects.

CHEMISTRY ? Clenbuterol is a ?2 adrenergic agonist with some similarities to ephedrine, but more potent and longer-lasting effects as a stimulant and thermogenic drug. Clenbuterol is quickly absorbed (70-80%) body, and it remains in the body for awhile (25-39 hours). As a result of its long half life, the adverse effects of clenbuterol are often prolonged.

EFFECTS ? Clenbuterol increases aerobic capacity, CNS stimulation, blood pressure, and oxygen transportation. It also increases the rate at which fat and protein is used up in the body at the same time as slowing down the storage of glycogen. It produces bronchodilation, stimulating the beta2-adrenergic receptors on bronchial smooth muscle. It also stimulates beta2-adrenergic receptors in other tissues, as well as beta1-adrenergic receptors, producing adverse cardiovascular and neurological effects, such as heart palpitations, muscle tremors, and nervousness. The beta-adrenergic receptors? activation accounts for clenbuterol's ability to increase lean muscle mass and reduce body fat.

DOSES ? Clenbuterol's recommended dosage is 0.02-0.03 mg twice daily. When prescribed, it is usually used in dosages anywhere from 20-60 micrograms a day. A dose of about 150 ?g should never be exceeded in a day. It is typically used by athletes and bodybuilders at a dose of 60-120 ?g per day, but it is Clenbuterol abuse. Clenbuterol is usually used in liquid form in equestrian usage.

On the Internet, clenbuterol is available in tablet, syrup, and injectable forms. It is purportedly obtained by illegal importation from other countries.