One of the forms of phophodiesterase is termed PDE5. The prescription PDE5 inhibitors sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP to degrade. CGMP specific phosphodiesterase type 5 causes the smooth muscle of the arteries in the penis to relax, allowing the corpus cavernosum to fill with blood. "This is very exciting -- the researchers have been working on this for a long time in a variety of different organs. It's not yet clinically available, but if it works and proves safe and effective, it would be a tremendous advance," said Dr. Ira Sharlip, a spokesman for the American Urological Association and a clinical professor of urology at the University of California, San Francisco. Licensed Pharmacy Viagra where to buy viagra without prescription Psychological factors are responsible for about 10%-20% of all cases of ED. It is often a secondary reaction to an underlying physical cause. In some cases, the psychological effects of ED may stem from childhood abuse or sexual trauma. However, the most common psychological causes of ED include:
