Roommate is smoking marijuana with her friends in our unit. What should I do?

I can't stand the smell and don't feel comfortable that drugs are being used in my apartment. I only met her once. I told one of her friends that I couldn't have people smoking marijuana in my apartment. I feel bad about possibly having to call the cops on her, but I feel like I have a right since they are doing something illegal where I have to live. I work with law enforcement too, so if there is anything left in the living room and the police know, I could get the blame.