Its called tough love, put your foot down, get him into a rehab. People who are addicted to drugs do not see how they are hurting themselves or people around them, and if they dont want to get help then there is nothing you can do to convince him what he is doing wrong. So you can tell him if he continues he will need to live somewhere else or go into rehab. It isnt easy for a parent to do this to their child, but sometimes you have no choice if you want to save them before he destrpys your family and his life.

I smoked for 7 years everyone tried to get me to stop but i loved it only because it helped my depression and made me not think so much but as years went on i did nothing and let things go it has messed up everything i ever wanted to be cause it made me lazy and sleep all the time.you should get more involved with him go hang out and eat with him let him know you care and show him pictures of what it can do to your lungs.If that does not work then put your foot down tell him he will stop and you will know cause you can buy home drug test at wal-mart or drug stores.You must not give up or he will get up hie future and could end up in jail or as well as the cops coming to your home for a search if some neighbor calls.There is hope just try hard.It takes time to get over the withdraw but he can do it!