My daughter-in-law, a brilliant and profoundly promising young woman (magna cum laude, extremely high I.Q.--that sort of thing) got hooked on methamphetamine, ruined her life, abandoned her children (all less than 10 years old) and faithful husband, wrecked her health, and died homeless, sick, and miserable at a young age. Her children are still trying to recover from the horrifying trauma.
To paraphrase Harriet Tubman, anyone who would provide you with methamphetamine would sell you into slavery and send you to hell.
I am so sorry for you, your son and your grandchildren.
You may want to look into this book, “The Realm of Hungry Ghosts” by Gabor Mate. I’m not fully convinced by it, but it’s a powerful perspective and analysis of why addiction happens.