The studies looked at patients with alcohol dependence, depression, and schizophrenia, and each came to a slightly different conclusion, depending on the condition being studied. So there does not seem to be an easy or universal answer to the question of whether one drug or a combination is the best treatment option.
To read the studies, see the American Journal of Psychiatry at http://ajp.psychiatryonline.org/. For coverage of this issue in Psychiatric News, see http://pn.psychiatryonline.org/content/46/11/15.2.full. Additionally, Treatment Resistant Depression: A Roadmap for Effective Care, published by the American Psychiatric Publishing, addresses this issue. For purchase information, see http://www.appi.org/.