You should talk to him about it. Tell him how worried you are about him and how you want him to be safe. If he doesn't listen, tell your parents or guardians (If you haven't already) They will be a big help to your brother. That might help! I hope things turn out well
If he lives at home and has the product at home, your parents could be liable. Talk to him first. Then your parents. He probably won't change I his own and may be mad. He will eventually go to jail if he gets caught. He is lucky to have you in his life.
There's not much you or anyone can do while that's the lifestyle choice he chooses by choice to live. Until he wants help he will continue as he does & I know it's hard to stand by & watch but you don't have much choice. I'm sorry I can't be more helpful.