How old is your friend and how addicted is he or she? If your friend is under the legal age you could report them to a parent or someone who can do something about it. If you both are adults try not drinking or partaking in drinking around him or her and encourage others to do the same. Have a group of loved ones all talk to the friend about the concerns and if he or she is willing to get help there are medical ways to help so see a doctor to see what is best for your friend. Good luck and your friends lucky to have you care so much about their health.