It works for up to 36 hours. This will increase the supply of blood to the lungs and reduce the workload of the heart. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. If you ever need emergency medical treatment for a heart problem, the healthcare providers who treat you will need to know when you last took sildenafil. The penis is one of the areas where this enzyme works. If you prefer, you may contact the U.The normal dose when starting Viagra is 50 mg, as needed. The maximum dose of Viagra is mg each day. Doses above the maximum dose, such as mg per day, will increase the risk of side effects. Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. FAQs What to consider Cost 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. .
