A Chochrane Library review has found evidence of bias towards industry-sponsored drug trial studies, says a Sydney researcher.

Doctors' views about the effectiveness and safety of many medicines they prescribe may be distorted after a review found evidence of bias towards industry-sponsored drug trials, say researchers.

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 than non-industry funded research.

"Our analyses suggest the existence of an industry bias that cannot be explained by standard 'Risk of bias'," the authors wrote.

The authors note 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.

The Chochrane Library updated a previous 2012 review by adding to a new 27 drug trial studies.

In total their were 75 studies studies reviewed.

Those that were sponsored by industry had a 1.27 times higher risk for reporting favourable efficacy results and 1.34 times higher for 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 to 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.