Physicians "downgrade the credibility" of clinical trial reports if they believe them to have been funded by the pharmaceutical industry, a new US study shows.

Reporting in the New England Journal of Medicine (NEJM) this week, researchers from Brigham and Women's Hospital and Harvard Medical School, Boston, write that "the methodologic rigour of a trial, not its funding disclosure, should be a primary determinant of its credibility." However, their findings show that doctors lose confidence in a study when they know it to have been funded by a drugmaker and that they are less keen to prescribe drugs trialled in industry-financed studies.

For their investigation, the researchers developed hypothetical scenarios for evaluating the use of three imaginary new drugs in treating common medical problems. Since doctors say they frequently read only the abstracts when reviewing the medical literature, the researchers created abstracts describing trials of the drugs in which they varied the product being tested, the trial's methodological rigour - high, medium and low - and the funding source, which was either not mentioned, or given to be the National Institutes of Health (NIH) or a pharmaceutical company, with financial involvement in that firm on the part of the lead author.

Participants in the study were told that the hypothetical drug had recently been approved by the Food and Drug Administration (FDA) and was covered by insurance, and that the abstract was from a "high-impact" biomedical journal and written by academic physicians at established US universities.

Overall, the study participants were able to distinguish between low, medium and high-quality trials, and were reluctant to prescribe drugs which had been studied in weaker trials. However, the researchers also note that: "regardless of the actual study design, physicians were less likely to view a trial as having a high level of rigour if funding by a pharmaceutical company was disclosed than if no disclosure statement was included."

The doctors were also found to be 37% less likely to consider prescribing a drug if they knew that the study had been industry-funded than if they were given no information on its funding, and 48% less likely to consider prescribing a drug when the funding had come from industry rather than from the NIH.

And in comparison with NIH-funded trials, respondents were also less likely to describe industry-funded trials as "important," the researchers add.

Discussing these findings, the study authors note that "well-publicised controversies" related to industry-funded research may help to explain them. For example, “reports have emerged of trials that withheld critical data or that presented positive results while withholding negative results. Other concerns stem from reports of industry-financed articles that were ghostwritten or published primarily as instruments of marketing," they write.

However, they also point out that "despite the occasional scientific and ethical lapses," pharmaceutical companies have supported many major drug trials that have been of particular clinical importance, and warn that excessive scepticism about industry-funded trials could hinder the appropriate translation of the results into practice.

Drugmakers need to address the attitudes revealed by the study, they urge. Financial disclosure is important, but more fundamental strategies, such as avoiding selective reporting of results in reports of industry-sponsored trials, ensuring protocol and data transparency and providing an independent review of endpoints, are needed.

They also suggest that, with physicians in the study assigning the highest level of credibility to NIH-funded trials, more trials funded by the NIH or by the new Patient-Centered Outcomes Research Institute might reduce clinicians' scepticism and lead to more data-driven changes in practice. 

And partnerships between the NIH and industry might also serve this purpose, if their jointly-funded trials feature characteristics that are a routine part of NIH-funded trials, including data and safety monitoring boards, and public reporting of protocols, they add.