How to forget?

One of my really good friends is going through a break up right now and he loved her a lot but she didn't return the favor... he can't keep his mind off her and no matter how much he wants to forget about her no matter how much he drinks or smokes she's still there and I keep trying to tell him that's not healthy. I really care about his wellbeing and I'd like to see him happy again. Do you have any ideas that I could tell him to try and get his mind right again?