TUESDAY, March 8 (HealthDay News) -- Meta-analyses of drug studies, which are major reviews of published research, hardly ever include conflict-of-interest information from the original studies, researchers report.

"Most people know that the message has a lot to do with the messenger," said study senior author Brett Thombs, an assistant professor of psychiatry at McGill University and Jewish General Hospital in Montreal. "If we buy a new car, we want to know that someone other than the manufacturer thinks it works well and is safe . . . but a large proportion of drugs we use daily are evaluated only by the companies that produce them."

Guidelines require that conflicts of interest be disclosed when randomized controlled trials (considered the gold standard of science) are published, but there are no such guidelines for meta-analyses.

"We're suggesting that guidelines be updated to encourage meta-analyses to report conflicts of interest," said Michelle Roseman, lead author of the study, which is published in the March 9 issue of the Journal of the American Medical Association.

Although "we can't say for sure that a trial that has links to the pharmaceutical industry is biased, we know from the literature that that potential exists," said Roseman, who is a graduate student in psychiatry at McGill. "If there were a meta-analysis where most, or all, of the included trials were paid for or linked to the pharmaceutical industry, we would want to know that. We would have more confidence if there was a large independent trial as well."

Research has shown that positive results from drug trials are more likely to be published than negative ones and that trials funded by the pharmaceutical industry are more likely to be positive than those funded by other sources.

Just as important, meta-analyses tend to be cited more often than other studies and can disproportionately affect how practice guidelines are devised, experts say.

"Meta-analyses and other kinds of systematic reviews are often [used] to make decisions and judgments both by individual practitioners and by guidelines developers and pharmaceutical and therapeutic committees," said Dr. Susan Dorr Goold, a professor of internal medicine and health management and policy at the University of Michigan in Ann Arbor.

The Canadian researchers reviewed 29 meta-analyses, which covered data from 509 randomized controlled trials. About 62 percent of the 509 trials had their funding sources listed when they were published in the key medical journals. And more than two-thirds of those had been supported at least partly by the pharmaceutical industry.

In addition, about one-fourth of the trials had author disclosures and, of these, almost 70 percent had at least one author with ties to the drug industry.

Yet, the Canadian researchers found that none of the meta-analyses disclosed the original authors' ties to pharmaceutical companies and only two reported the original funding sources.

"Even in those two, they didn't mention this issue in the text of the article," Thombs said. "Neither were where most readers could see them."

Goold noted, "I don't think that we're going to give up industry-funded clinical research, [but] it might be a good idea to have additional disinterested funding support to sort of check things and verify validity. We know there's a profit motive. There's supposed to be a profit motive. I don't think drug or device companies are evil."

But, she added, "as recipients of knowledge, doctors or guideline writers need to be looking a little bit differently at research that's got that sort of funding relationship, [and] we need more data on what kinds of relationships have influence."

More information

The U.S. National Institutes of Health has more on clinical trials.