Drug possession

Awhile ago I went to visit one of my friends in another state, I noticed her roommate was on drugs cause first, he smelled like weed when he stepped in the car, and another time he was preparing some other drug I wasn't familiar with to snort. I was wondering if I called the police for him having would they tell my friend and him that the call came from my state? Would they arrest him or give him a fine? I don't want my friend to know I called the police on him, but at the same time I don't anything illegal happening.