<s>[INST] Hi, Im a 18 year old and have been taking a pre work out supplement called c-4. Ive been on it for a while now about 4 months and had no problems. But today for the first time I was unable to get an erections and I noticed that my main vein on top of my male reproductive organ would move and it normally never does. Im a bit worried. [/INST] Thanks for contacting ChatDoctorYou are concerned about having erectile dysfunction after taking C-4 supplements. In looking at what is in C-4 it has large amounts of nitrates that is supposed to help amp your energy levels up. This is cause erectile problems and I recommend that you stop taking C4 supplements and stay with high protein supplements. The erectile dysfunction will resolve once you stop taking the C4Hope this answers your question. Please contact us again with your medical concerns and questions </s>