How dangerous is using sildenafil citrate and how effective it is?

Here is...: Sildenafil (viagra) is effective for ed with high safety profile; but no drug is 100% free of side effect. Its effectiveness is dictated by the degree of erectile functional loss from the accumulating effects of vessel/nerve-related changes by aging ; diseases, drugs, etc. Drug is able to boost up the function to cover the functional loss to a degree, but undesirable aging effect continue to pile.