In my opinion it would be very beneficial for your friend to see a chemical abuse counselor. Telling the one at school is definitly a hard decision to make however in the long run i think that the best thing to do would be to talk to the counselor at your school. Friends help each other out and look out for each other. Even if your friend does not think that he/she has a problem, if you see it then they probably do. Your friend will appreciate it in the long run. The fact that his father died when he was young could have alot to do with the reason that he uses substances. He very well may have repressed feelings/emotions about his loss that he can not express. He is probably using pot & Alcohol as escapes. When ever a substance is used as an escape mechanisim it is almost an immediate signal the the individual is at risk for becoming an addict. This is especially true with Alcohol. So after my long winded opinion (sorry about that... We talked about similar case in class) talk to the counselor at the school and have him/her talk to your friend
Hope everything works out