Please Pray for my Teenage Son

I have 19 years of bright,gifted teenage son, who is in the senior year of college in CA. As marijuana is legal in CA, and with peer pressure he started using that last year. He is promising us that he will stop- but no result. Now he has stop email/phone connection with us(parents)- Please pray that God heals him and make my son free from substance abuse. God heals our relationship.
He talks openly with me(Mom) and Dad. God gives him guidance and put him back on right path in the life- and he completes his study. I need miracle for my son. I want him back in my life - Happy, healthy, bright, loving, peaceful son.
Thank you for your prayer.- (Mom)- K Rai