Years of research have been dedicated to answering this very question. We can confidently say that therapy has been demonstrated to be an effective means for individuals and families to get relief from emotional distress and to make meaningful changes in their personal and family lives. In fact, in most cases, therapy is shown to be as effective as medication for many emotional disorders such as anxiety and depression. In other cases, psychotherapy in conjunction with medication has been shown to be the most effective intervention; for example, in the case of ADHD or ADD.
For more information on the effectiveness of therapy, see the following websites:
APA Practice Directorate (September, 1994) www.apa.org/practice/peff.html