Clenbuterol Hydrochloride (Clen) is a bronchodilator that was created to treat breathing disorders, mostly asthma. The drug has never been approved by the US FDA because there were already several very similar medications, with almost identical properties, which had already been approved in the US by the time Clenbuterol was released. However, Clen is legalized in lots of countries around the world, including European Union countries, as an asthma drug.