A systematic review has found "evidence" that industry-funded studies are more likely to favour products of pharmaceutical companies than independent research.
Doctors' views about the effectiveness and safety of many medicines they prescribe may be distorted, researchers say, after a review found evidence of bias towards industry-sponsored drug trials.
Professor Lisa Bero of the University of Sydney's Charles Perkins Centre says a new Chochrane Library systematic review has found "definitive evidence" that studies are more likely to favour products of pharmaceuticals and medical devices firms than non-industry funded research.
However, Milton Catelin, chief executive of Medicines Australia, disagrees, saying the rules that govern clinical trials in Australia are rigorous.
"Bias is a factor that our system considers, right up to pricing and reimbursement of a medicine in all clinical trials in Australia. As an industry, we also abide by an internationally harmonised framework," Mr Catelin said.
He said clinical trials are evaluated through a lens of "risk and reward" and are essential to ensuring Australians have access to life-saving medicines.
The Chochrane Library updated a previous 2012 review by adding 27 drug trial studies to be analysed. In total, 75 studies were reviewed.
Those that were sponsored by industry had a 1.27 times higher chance of reporting favourable efficacy results and a 1.34 times higher chance of reporting favourable conclusions.
According to the the research, drug industry-sponsored studies were about 30 per cent more likely to have favourable results and conclusions.
Co-author of the review Dr Joel Lexchin, Professor Emeritus of York University, said the findings were especially concerning for patients and doctors.
"Our views about the effectiveness and safety of many medicines may be distorted. 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," he said.
"Our analyses suggest the existence of an industry bias that cannot be explained by standard 'risk of bias'," they wrote in the review.
The authors noted there are several potential ways that industry sponsors can influence the outcome of a study, including the framing of questions, the design of a study and how data is analysed.
Some medical journals require that the role of the sponsor in the design, conduct and publication of the study be described, but this is not widespread, said Prof Bero.
"We need bias assessments tools for drug studies that take funding source into account," she said.
John Zalcberg, chair of the Australian Clinical Trials Alliance, said the review actually raised many unanswered questions.
He said while a bias was found, the authors of the review were unable to identify the cause of the bias.
"We need to be cautious but we still don't know much about the bias," Professor Zalcberg told AAP.
He said most doctors look to randomised control trials to inform best practice.
"This was a review of papers that review studies," Prof Zalcberg added.