This seems like a tough situation. If your friends' use of drugs etc. is making you uncomfortable and making hanging out with them not very fun, then you might want to consider finding other friends. I mean you could still hang out with them but know there are other options. It is a pretty difficult task to change the habits of your friends. Maybe you should talk to them about your feelings or at least just talk to the ones you are closest with. There is no reason to use drugs and alcholol just because your friends are doing it, but if that is all they do then I know it becomes hard to refrain.

Maybe you should try to spend time with them when you know they will not be messed up and enjoy them at these moments. I don't think your friends are bad people for using drugs but it is hard not be concerned for them at some level. You shouldn't have to lose them because of their habits but you just have to find the right balance that allows you to protect yourself and do what you want to do. Good luck and try to stick to your own values while knowing that you deserve to keep your friends.