Aim: To investigate whether adverse effects data for the sponsor's product are presented more favourably in pharmaceutical industry-funded studies than in non-industry-funded studies.
Methods: We conducted a systematic review of methodological evaluations that had assessed the relationship between industry funding and the reported risk of adverse effects. Searches were undertaken in 10 databases and supplemented with other sources of information such as handsearching, citation searching, checking conference proceedings and discussion with experts. Two reviewers independently screened the records and carried out data extraction for potentially relevant papers. We included studies that compared the results and interpretation of the adverse effects data according to funding source (e.g. adverse effects data in pharmaceutical industry research vs. data from nonprofit organizations, or from one manufacturer vs. another). Methodological evaluations were excluded if categories of funding source were not explicitly specified by the researchers, and if we were uncertain that industry-funded studies were present in the evaluation.
Results: The search strategy yielded 4,069 hits, of which six methodological evaluations met our inclusion criteria. One survey of 370 trials covering a wide range of topics found that trials with industry sponsors had more complete reporting of adverse effects compared with non-industry-funded trials, whereas another survey of 504 inhaled corticosteroid studies showed no apparent difference after confounding factors were adjusted for. In contrast, we found evidence from post hoc subgroup analyses involving two products where the likelihood of harm was of a lower magnitude in manufacturer-funded studies compared with nonmanufacturer-funded studies. There is also evidence from four methodological evaluations that authors with industry funding were more likely than authors without pharmaceutical funding to interpret and conclude that a drug was safe, even among studies that did find a statistically significant increase in adverse effects for the sponsored product.
Conclusions: Our review indicates that industry funding may not be a major threat to bias in the reporting of the raw adverse effects data. However, we are concerned about potential bias in the interpretation and conclusions of industry-funded authors and studies.