To our knowledge, this is the first study to systematically appraise pharmaceutical press releases. Our large sample provides useful information about the quality of press release reporting of original research.
Our study shows that industry press releases are generally good at providing basic study details, but may provide incomplete information needed for a reader to gauge a study's clinical implications. Many press releases focused on research presented at scientific conferences, often considered the forefront of current knowledge. However, this information is frequently based on preliminary data without peer-review and may omit limitations such as small study size, uncontrolled study design or short duration of follow up 
. In turn, this can mislead readers about the validity of results 
. Furthermore, several releases were not explicit about the source of original data and only a fraction noted any study limitations. A third of releases did not quantify study results, and of those that did, results were presented using a ratio measure - a format known to exaggerate the perceived magnitude of effect 
It is not surprising that randomized controlled trials were overrepresented in press releases as these studies have considerable influence on clinical practice. In addition, widespread illnesses such as heart disease, cancer and HIV/AIDS were the most cited medical disciplines. Previous work has shown that medications used to treat chronic disorders are the focus of considerable advertising efforts by pharmaceutical companies and may garner more media attention 
We found no other work evaluating press releases from pharmaceutical companies. However, Woloshin et al. examined the quality of press releases issued by medical journals 
. Similar to our data, they found that releases do not routinely highlight limitations and often use formats that exaggerate study findings.
Our study has several limitations. First, we only examined archived releases for the year 2005 available in electronic format on corporate websites. This led to the exclusion of fifth-ranked Merck & Co. While results may not be generalizable to smaller drug companies, we selected the world's most successful pharmaceutical manufacturers who all have strong media presence and public relations practices. Second, we did not corroborate press release content with subsequent publication, as our aim was to report study characteristics rather than test data accuracy. This approach may be justified as previous work has shown that abstracts often differ from published peer-reviewed results. In a study examining transition of scientific meeting abstracts to full-length journal article, 41% of publications exhibited significant discrepancies when compared to the original abstract data 
. Third, the findings are predicated on our construct of what constitutes a good quality press release. Our instrument was based on previous work and established guides but results may differ with other assessments tools. Lastly, while we know that journalists frequently rely on press releases as a source of health topic ideas, the association between releases and ensuing coverage in newspaper, radio or television stories was not investigated 
Our findings suggest that the quality of pharmaceutical press releases needs improvement. Simple ways of enhancing quality would include referencing original data to confirm press release content, quantifying study results in clinically meaningful ways, and identifying important limitations so that the generalizability of results across different populations and settings can be appreciated.
It is unlikely that the pharmaceutical industry will change its reporting of original research. Thus, journalists and newsmakers should be aware of the shortcomings of press release data and learn to scrutinize this information before adoption into health news for public consumption. Creating a standardized “checklist” of quality indicators is one possible appraisal tool for readers to use.
Future studies should explore the process by which press release content is selected, edited and later distributed. As with all health information, critical review is essential to contextualize its content.