Hi, I'm really sorry your going through this. I'm not sure what advice I can give you.
Other than keep reaching out to him, and be there for when he wants your help.
At about the age of 16 I started using drugs and drinking excessively. The reason for this was I really struggled with life, felt like I didn't fit in with anyone, didn't know what I wanted in life, struggled with undiagnosed depression and anxiety and ended up falling in with the wrong people, drinking and taking drugs. I took my stuff and left home at 18 but my parents never stopped reaching out to me.
For me what was unhelpful was the labels and things my family said about me, for example, alcoholic, druggy, selfish, disgusting, and more. My parents were obviously desperate to get me back and safe but all these things they would say made me feel misunderstood and like I could never ever speak to them honestly.
What was helpful in the end was looking into the reason behind why I wanted to use, instead of focusing on the actual drug use.
Someone found me a substance misuse service in my area that worked with me, and explored all these things. Maybe you could speak to a GP or look up if there are any substance misuse services in your area and see if your son can engage with them?
When I worked with services I didn't stop straight away but they gave me an education around drugs that kept me safe and gave me information that potentially saved my life? If you could get something for your son, education around drugs maybe really helpful so he knows how to keep himself safe.
Maybe it's also worth looking into what services are available for parents in your area, so you could get some support and expert advice?
I stopped smoking, taking drugs and drinking alcohol completely almost 3 years ago. I hit a rock bottom, and reached out for help, and my family where there when I did and I'm glad for that. Just don't give up on him, and be there for when he wants the help, also really recommend looking into substance misuse services and if there's anything that is especially for young people.
I really hope things get better for you and your family and wish you the best of luck.