Researchers from the University of Sydney published a review this week, concluding that industry-funded drug trials are often biased in favor of the sponsors’ products.

According to Lisa Bero of the university’s Charles Perkins Centre, the study provides “definitive evidence that pharmaceutical industry funding of drug studies biases the results and conclusions to look favourable towards the drug of the sponsor.”

Compared to non-industry funded studies, industry-sponsored drug and medical device studies more frequently reported results that were more favorable to a sponsor’s product and more often had positive overall conclusions. In a group of 75 studies, the authors found that industry-funded studies had less agreement between their results and overall conclusions compared to their counterparts.

The authors wrote that there are many ways that industry can influence the outcome of a study – they could bias the design or conduct of the study or selectively report favorable results.

Although some journals take a proactive stance to make the role of study sponsors more transparent, the practice is not widely-held amongst all scientific journals.

“We need bias assessment tools for drug studies that take funding source into account,” Bero said. “Currently, we have no validated way to detect or evaluate these subtle but systematic biases.”

“Our views about the effectiveness and safety of many medicines may be distorted,” co-author Joel Lexchin added. “Medicines may be both less safe and less effective than we think to the extent that the evidence about them comes from the companies making them.”

Last month, a study conducted by a team of U.S. researchers found that financial ties between researchers and the companies that make the drugs they are studying are independently associated with positive trial results. The team’s work was published in The BMJ.

Both studies were observational, so their results can’t be used to draw concrete conclusions. But the authors write that since industry and academia collaborate to advance many new treatments, “more thought needs to be given to the roles that investigators, policy makers, and journal editors can play in ensuring the credibility of the evidence base.”