Alcohol absolutely makes you feel worse, and can make your symptoms temporarily worse, but I don't believe it causes anything permanent (other than, you know, the fact that excessively consuming alcohol in general is not good for your brain, concussion or not.)

I have drank too much on several (stupid) occasions during my recovery, and each time it has been terrible for my mood swings, brain fogginess, etc in the short term. However, I'm always able to recover after resting, eating healthy, getting enough sleep, etc. for a few days to a week afterward. I really would recommend either cutting out alcohol completely or keeping it to one drink every once in a while, because you'll feel better if you do. I know it's hard when you have friends that drink a lot, though, coming from personal experience.