Can/will a therapist tell my parents about drug use?

I'm 18 turning 19 in June and am going to start seeing a therapist over the summer. I've never had a therapist before so I don't know what they can/cannot say to my parents. Although I'm a legal adult, I know for most drugs you have to legally be 21+ to purchase or be in possession of them so I'm not sure if my drug use is something that should be brought up to the therapist.