TA, Welcome! It is extremely difficult to watch our children destroying themselves. Addicts will do whatever they need to do to get the next fix . As addicts (and I am a recovering addict who got clean and sober at 24 years old and have never had a need to pick up another drink or drug since by the grace of God and the rooms of NA and AA) we live to use and use to live. And that is where your son is at.
The very best thing you can do for him is nothing . Let him live the way he currently does because as bad as it feels to you, he has to get worse before he can make a choice to get better . Pray for him if you have a belief in a Higher Power and allow God to work in his life. Never give up hope. I just heard the story of an AA member with 30+ years sober and he lived in a shed at the height of his alcohol and amphetamine abuse . He finally had enough when he had run out of all options and his girlfriend at the time dropped him off at an AA clubhouse. Do not give him money or resources as it will enable him to continue destroying himself. If he contacts you in a state of remorse, guilt, and being hungover (the only time you might have a chance to reach him) , tell him you cannot help him but you know someone who can and give him the AA or NA help line in your area
In the meantime, it is of utmost importance that you help yourself. It will sound counter intuitive right now , but you can help your son the best when you learn how to take care of you and demonstrate that by doing it .Please , please, please go to Al-Anon meetings for yourself. Commit to 6 meetings before you make a decision whether they are for you .It has helped me more than anything ! Start tending to yourself slowly, in baby steps, physically, emotionally, and spiritually . When you take the focus off your son and place it on you, you are helping him more than you can know right now.
Please keep reaching out to us . Post here when you want to go enable him and keep in mind that the disease of addiction is a huge mountain of a disease only relieved by spiritual intervention, so when we stand next to the huge mountain addiction is in our small body suits and a small (comparatively) shovel thinking we can even make a dent in the disease of someone else, we are so sorely mistaken. Take care of yourself. Sending love and light and praying for you and your son.