beating him up and telling him seriously how bad his life is going to be if he doesn't quit. it worked for one of my other friends. how is his relationship between the dad? if its bad then thats a plus because you can always say he will turn out like his dad. anyways heres some facts.
"Marijuana is the most commonly abused illicit drug in the United States."
" Long-term marijuana abuse can lead to addiction for some people; that is, they abuse the drug compulsively even though it interferes with family, school, work, and recreational activities. Drug craving and withdrawal symptoms can make it hard for long-term marijuana smokers to stop abusing the drug. People trying to quit report irritability, sleeplessness, and anxiety. They also display increased aggression on psychological tests, peaking approximately one week after the last use of the drug."
both are quoted from http://www.nida.nih.gov/Infofacts/marijuana.html
there you can also find a section that tells about what to do if someone you know is addicted/abuses drugs
"smoke two joints" by sublime