I went through this with my daughter. However she was 13 and in school when it all began (she was in school when she took a few oxys; the first time). Trust your instincts. Every time I felt something wasn't right, it wasn't. She was self-medicating (bipolar, etc. was eventually her diagnosis).
I set boundaries and I stuck to them. I'd take her to the police department if needed. I did what I had to do as a parent until she turned 18 and I was no longer responsible. It was extremely stressful for a few years, but we made it through it. What kept me sane was telling myself, "what will be, will be. it's in God's hands" ...and I prayed for her safety.
Today she is 21 and has thanked me numerous times for not giving up on her. I hope for the best of outcomes for you, your son and your family.