I first saw this film when I was recovering from heroin addiction myself, so the scene where Jesse's friends take him for a holiday in the woods to detox was particularly moving for me and, I think, realistically portrayed.
The film features a lot of fairly explicit violence and is not for kids. Stoltz and Thornton both act their socks off and are totally convicing. The supporting cast are excellent too.
Buy this movie and I promise you will not regret it. Maybe not an all-time classic but a film you will remember and want to see again in the future.