Background: In recent years, a number of studies have shown that clinical drug trials financed by pharmaceutical companies yield favourable results for company products more often than independent trials do. Moreover, pharmaceutical companies have been found to influence drug trials in various ways. This analysis provides an overview of the findings of current, systematic studies on the topic. Methods: Publications retrieved from a systematic Medline search on this topic from 1 November 2002 to 16 December 2009 were independently evaluated and selected by two of the authors. These publications were supplemented by further articles found in the reference sections. Results: 57 publications were included for evaluation. Published drug trials financed by pharmaceutical companies were found to yield favourable results for the drug manufacturer more frequently than independently financed trials. The results were also interpreted favourably more often than in independently financed trials. A number of studies revealed that many trials financed by pharmaceutical companies are never published and that favourable results are published multiple times. Further studies showed evidence of other problems including influence on study protocols, incomplete trial registration, constraints of publishing rights, withheld knowledge of adverse drug reactions, and the use of ghost writers supplied by the pharmaceutical companies. The methodological quality of trials financed by pharmaceutical companies was not found to be any worse than that of trials financed in other ways. Conclusions: Published drug trials financed by pharmaceutical companies may present a distorted picture. Public access to trial protocols and results must be ensured. Moreover, more effort should be made to carry out drug trials independently, without the financial support of pharmaceutical companies.



Full title: The Financing of Drug Trials by Pharmaceutical Companies and its Consequences. A Qualitative, Systematic Review of the Literature on Possible Influences on the Findings, Protocols, Quality, Authorship, Access to Trial Data, Trial Registration and Publication of Drug Trials