I wouldn't think a 500mg/wk for 12 week cycle would produce significant erectile dysfunction if the cycle is run properly. I would be worried about the affect the Test will have on your brain development. Not being funny, the average male's endocrine system, the stuff that controls the natural production of about 100 hormones, does not mature until mid 20's. Taking exogenous Test or other Test related products can affect the development of your endocrine system. This could cause ED or other sex related issues. Then again, like Samson said, it depends.