There are several ways that you can stop a mate from drinking if you think that he has a problem with it. The first step (as you probably already know) is to get them to recognize that they have a problem. Once they admit they have an issue, you can ask them to see their doctor about it (who will give the best advice). There are several other steps that you can take, and you can check them out here. Other than that, you should know that by completing your RSA course online, you will learn about responsible service of alcohol and some valuable tips on how to identify when someone has had to much to drink.