Co-Occuring disorders, what disorder should be treated first mental health or substance disorder?

You are a professional and you have a client who has a co-occurring disorder, which disorder would you as a professional treat first and why? As a professional would you diagnose and/or treat a co-occurring personality disorder? If so why and if not, why not? Please include ethical, legal and socio-cultural implications of the treatment decisions you as a professional has made. In text citation, APA 10 pages