The trial registry ClinicalTrials.gov, which permits posting of trial results, includes results of some trials that have not been published in a peer-reviewed journal and in some cases includes more information than published trials, according to Carolina Riveros (INSERM, Paris, France) and colleagues, authors of a PLOS Medicine study published this week. The researchers searched ClinicalTrials.gov on March 2012 for randomized controlled trials of drugs with posted results. They selected 594 of these trials at random and searched PubMed for corresponding publications. Of the trials, 297 (50%) had no corresponding published article, despite the unpublished trials having a median year of completion of 2009.

Some outcomes were significantly more likely to be posted on ClinicalTrials.gov than published in the article; these were flow of participants (64% [129/202] vs. 48% [96/202] of trials, p<0.001), efficacy results (79% [159/202] vs. 69% [140/202], p=0.02), adverse events (73% [147/202] vs. 45% [91/202], p<0.001) and serious adverse events (99% [199/202] vs. 63% [127/202], p<0.001).

The authors state, "Our results have important implications for several stakeholders: patients and clinicians, authors, researchers performing systematic reviews and meta-analyses, methodologists, peer reviewers, developers of reporting guidelines and journal editors… our results outline the importance of registries to improve transparency in clinical research by making information about clinical trials including results publicly available, which is the basis for well-informed decision making about patients' health."

The authors acknowledge that unpublished trial results could be published at a future date; some trials may be submitted for publication several years after completion. They conclude, "our results highlight the importance of extracting efficacy and safety data posted at ClinicalTrials.gov for trials whose results are not yet published but also for those with published results because we found that reporting was more complete at ClinicalTrials.gov. Use of templates allowing for standardized reporting of trial results in journals or broader mandatory registration of results for all trials may help further improve transparency."