This is an issue I had to deal with for a long time. My cousin, who I am very close with, is a recovering heroin addict. Until they hit rock bottom, there isn't much you can do to help. My cousin OD'ed and spent a week in a coma, and that was his rock bottom. When he woke up, he was so grateful to be alive that he finally decided to face his problem. He turned himself in for the felony drug charges against him and spent some time in prison, but that time in prison helped him a lot. It gave his life some much needed structure while he recovered from his addiction. It also gave him additional motivation to never use again. He's been sober for almost 3 years now and is studying to become a mechanical engineer.
It's important to remember that when you think you might be helping him, you might actually be hurting him. The best thing you can do safely steer him towards rock bottom. That is the only thing that will convince him that he needs to help himself. The longer he stays hooked, the less likely he will ever be able to get sober again.