I'm not going to tell my parents about my brother's drug use
Why do you want to hide that from them?
They won't find out and he'll be safe for now.
If your brother has a drug problem, you should get him some help. He isn't safe if he's using drugs irresponsibly. If you can't tell your parents, try to tell a trusted adult or get him counseling or rehab.
I'll just keep him away from the drugs, and then get him treatment later.
You should tell someone that can help him, though. You might not be able to deal with drug withdrawal. It could be dangerous for him.