Unpublished trials of alprazolam XR and their influence on its apparent efficacy for panic disorder

To test for publication bias with alprazolam, the most widely prescribed benzodiazepine, by comparing its efficacy for panic disorder using trial results from (1) the published literature and (2) the US Food and Drug Administration (FDA).

From FDA reviews, we included data from all phase 2/3 efficacy trials of alprazolam extended-release (Xanax XR) for the treatment of panic disorder. A search for matching publications was performed using PubMed and Google Scholar. Publication bias was examined by comparing: (1) overall trial results (positive or not) according to the FDA v. corresponding publications; (2) effect size (Hedges's g) based on FDA data v. published data.

The FDA review showed that five trials were conducted, only one of which (20%) was positive. Of the four not-positive trials, two were published conveying a positive outcome; the other two were not published. Thus, according to the published literature, three trials were conducted and all (100%) were positive. Alprazolam's effect size calculated using FDA data was 0.33 (CI_95% 0.07-0.60) v. 0.47 (CI_95% 0.30-0.65) using published data, an increase of 0.14, or 42%.

Publication bias substantially inflates the apparent efficacy of alprazolam XR.