Methadone is a tried and true way to lessen the harsh drop off of heroin. Do you read much? I am reading a fascinating page turner that addresses addiction very well. The book is called Trejo. As in Danny Trejo. Famous actor, restauranteur and addiction counselor. Maybe your library has it. Maybe if you like it your son might read it.
You'll have to read but as he knows, reading is good for you:
https://www.amazon.com/Trejo-Life-Crime-Redemption-Hollywood-ebook/dp/B08QJRPJWR