With meta-analyses exerting a growing influence on drug policy and prescribing decisions, it is imperative that these reviews provide high-quality, transparent and unbiased evidence.

Yet, warn researchers from Canada, the US and the Netherlands in the latest issue of the Journal of the American Medical Association (JAMA), funding sources and financial ties are rarely mentioned in this context, to judge by a review of 29 meta-analyses on a range of drug treatments recently published in high-impact medical journals.

The team led by Dr Brett Combs, assistant professor in the Department of Psychiatry at McGill University in Montreal, Canada, and Michelle Roseman, a McGill graduate student, selected the three most recent meta-analyses of patented medicines published between January and October 2009 in general medicine journals with an impact factor of at least 10; high-impact journals in the five specialities with the highest sales of therapeutics worldwide in 2008; and in the Cochrane Database of Systematic Reviews.

The 29 meta-analyses reviewed included results from 509 randomised controlled trials (RCTs). The researchers found that only two or 7% of the meta-analyses reported funding sources for the clinical trials, while none of them disclosed author-industry ties for the RCTs or any details of employment by the pharmaceutical industry.

Of the 318 meta-analysed trials that originally reported funding sources, 219 or 69% were funded by industry and 91 (69%) of the 132 RCTs that featured author financial disclosures included one or more authors with financial ties to the pharmaceutical industry.

In seven of the 29 meta-analyses reviewed by Comb, Roseman et al, all of the RCTs included had at least one type of disclosed conflict of interest (pharmaceutical industry funding, author-industry financial ties, employment), yet only one of these seven meta-analyses reported RCT funding sources and none of them disclosed author-industry ties or employment.

“What is surprising is that many researchers who do meta-analyses don’t seem to be aware of these important issues,” Roseman commented. “We surveyed the authors of the 29 meta-analyses. Only seven said that they even recorded who funded the drug trials they evaluated, and only two published this information. Furthermore, only two recorded author-industry financial ties, and none published this.”

Researchers conducting meta-analyses “should be aware of who funds the trials they review and they should assess the risk that findings might be biased due to drug company sponsorship”, Roseman argued.

The review published in JAMA was supported by funding from the Canadian Institutes of Health Research and the Fonds de la Recherche en Santé Québec.