Publication and outcome reporting of homeopathy trials registered in ClinicalTrials.gov

Background: Homeopathy is gaining popularity globally, despite a lack of convincing evidence of its efficacy. For example, a 2015 review by the Australian National Health and Medical Research Council (NHMRC) found no discernible convincing effects beyond placebo. However, a concern was that publication bias and outcome reporting bias could have influenced the results of the included systematic reviews. Objectives: To study (i) the rates of non-publication and (ii) rates and types of alteration of planned outcomes of homeopathy studies registered on ClinicalTrials.gov. Methods: We searched ClinicalTrials.gov for all homeopathy trials completed more than 2 years ago. We then checked the trial's publication status by examining the publication field in ClinicalTrials.gov, searching PubMed and finally Google Scholar. We also checked whether the registered primary outcome matched the published primary outcome. Results: We found 35 registered homeopathy trials, from 11 countries, completed at least 2 years ago. Of these 35, we found 16 (46%) publications in MEDLINE and Google Scholar. In four (of 16), the primary outcome measures had been switched or modified. Conclusions: Of all homeopathy trials registered on ClinicalTrials.gov, only 46% appear to have published within 2 years of completion, of which a quarter altered their primary endpoint. Further research is warranted on the nature and reasons for non-publication.