Tadalafil is an orally administered drug used to treat male erectile dysfunction (impotence). It was initially developed by the biotechnology firm ICOS and subsequently developed and marketed worldwide by a joint venture of ICOS Corporation and Eli Lilly and Company (Lilly ICOS LLC) under the brand name Cialis. Cialis tablets are yellow, film-coated, and almond-shaped; produced in 5, 10, or 20 mg doses.In the United States, tadalafil has Food and Drug Administration approval and became available in December, 2003 as the third impotence pill after sildenafil (Viagra) and vardenafil (Levitra). Due to its 36-hour effect it is also known as the weekend pill. As with sildenafil and vardenafil, it is recommended that tadalafil be used no more than once daily. Tadalafil is also currently undergoing Phase 3 clinical trials for the treatment of pulmonary arterial hypertension.