Gabapentin in the Treatment of Mental Illness: The Echo Chamber of the Case Series

Background. Bipolar disorder is a common and debilitating psychiatric illness. Several antiepileptic drugs (AEDs) have been approved for the treatment of bipolar disorder. Gabapentin gained a large market share of AED use in the late 1990s in spite of a lack of randomized clinical trial (RCT) evidence and no labeled indication from the U.S. Food and Drug Administration for its use in psychiatric illness. This article describes the results of a literature review, the purpose of which was to examine the characteristics of studies conducted in humans concerning the efficacy of gabapentin in bipolar disorder. Methods. Publications relevant to this topic were identified based on a PUBMIED search as well as an examination of references from a published systematic review and citations from relevant review articles. Results. The search located 29 studies published between 1997 and 2007, with the greatest number of articles published in 1998 and 1999. Of these 29 publications, 15 involved uncontrolled case series, while 6 were single case reports. The sample size in the studies was generally small, and often we could not identify the funding source. Despite the generally weak study design in the identified publications, the authors of the articles often commented on the promising nature of gabapentin therapy for bipolar disorder. However, 4 small, randomized trials in heterogeneous populations demonstrated little if any evidence of such efficacy. Nine letters to the editor demonstrated a similar pattern. Conclusions. The large number of case series concerning gabapentin is striking. The number of reports and their distribution in many different journals created a type of echo chamber effect, through which the sheer number of publications and citations may give legitimacy to the practice of using gabapentin for bipolar disorder. Although the case series were generally of poor quality, their publication in peer-reviewed journals may have been partially responsible for the widespread use of an ineffective medication. (Journal of Psychiatric Practice 2007;14(suppl 1):15-27)