You can try to go about this many ways. You can try to heal the addiction, which I personally like the idea of. You could try cleansing them of the influence the lure of alchohol has over them. You can even try to write a spell used to make them feel discusted at the site/taste of alcohol. There are various things you could try/do. However, it might be more effective for you to have an intervention with this person. Help them understand how you feel and the people around them feels.
Maybe use a protection spell to ensure that they don't hurt themselves or other people. I agree though that an intervention is probably your best bet. In the end, only the person drinking can really change his or her habits.