Orally active drugs have been used for the treatment of men with erectile dysfunction (ED) since the 1980s. Agents such as yohimbine had poor efficacy and it was not until 1998, when sildenafil was approved as a licensed drug in the United States, that effective oral treatment for men with ED became widely available. Subsequently, several similar phosphodiesterase type 5 inhibitors have been approved for clinical use, which have consistently demonstrated high rates of efficacy, and excellent tolerability, in clinical use.