I can say when it kicks in it is effective. I have mild to moderate ED from diabetes and it does allow me a very sufficient erection when it works. There are a number of factors in its' efficacy. What you eat has a big role in whether it will help for example. The interesting thing about Viagra is that it has tell tale side effects that let you know it is working. Your color vision changes. Blues get more vibrant. Once it kicks in you have one hour to get the work done. It fade pretty quick after that.