I think my son might be a drug addict
What makes you think that your son is a drug addict?
He has been staying out all night lately.
Being concerned about your son is one thing, but do not make assumptions. He might just be studying with them, ask him straight out. Don't settle for just guessing because it might insult him for something he doesn't do.
No way he's been staying out all night with them. End of discussion.
You should probably go ahead and have a conversation with your son about why he is staying out. Assuming he is doing drugs or something like that is unfair.