See Doctor Now. mg of Sildenafil (Viagra) is the highest dose prescribed. Your doctor decides what treatment is best for you. Different dosages all work the same way and last .Do not stop taking sildenafil without talking to your doctor. If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. Without physical action to the penis, such as that occurring during sexual intercourse, sildenafil will not work to cause an erection. Don’t let ED ruin your fun – get help, today! Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. · Revatio Viagra Descriptions Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines . Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a . See Doctor Now. mg of Sildenafil (Viagra) is the highest dose prescribed. Your doctor decides what treatment is best for you. Different dosages all work the same way and last .Some medications should not be taken with sildenafil. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. Do not keep outdated medicine or medicine no longer needed. Sildenafil usually should not be taken more than once every 24 hours. However, the dose is usually not more than 80 mg 3 times a day. Do not use more of it and do not use it more often than your doctor ordered.