There has never been a reason for me to address the therapist by any name. There are only two of us in the office. If I ever had a reason to address a therapist by name - I would use their first name unless the therapist wanted to use formal titles for both of us- then I would use her last name and I would expect her to use mine. I feel that way about any professional I hire. I don't call mds "doctor" if they call me by my first name. We will either all be informal and familiar or we all will not.

The two I saw recently were lcsw's - I have more education than they do. I saw one who had a phd - she was batshit crazy. If I had needed to address her by name - I would have used her first name.