What is Grey Literature?

The definition of grey literature is: “That which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers1.”

Some reasons to search for grey literature are:

  • Minimizing publication bias when conducting a systematic review
  • Finding studies that have not yet been published, and possibly may never be published
  • Uncovering data for health technology assessments and economic evaluations

Finding grey literature can be challenging for a number of reasons. First, there isn’t one database that can find all of the grey literature on a specific topic. Also, managing and citing the references can be a bit tricky because most grey literature resources do not have a good way to export citations into citation management software. And finally, grey literature resources might frequently change by removing data, so the search can yield different results when searched on different dates.

There are many places to find grey literature. Some of the major categories are:

  1. Clinical Trial Registries
    • Clinicaltrials.gov– Since 1997, human trials were required for experimental drugs sold in the US, and the requirement extended to devices and biologics in 2007
    • Other national trials registries: This guide created by the University of York gives a list of many clinical trials registers and some tips for searching each one
  1. Government or Organizational Resources
  1. Dissertation and Theses
  1. Conference Abstracts
    • Many databases, such as Embase and the Cochrane Central Register of Controlled Trials (CENTRAL), now cover some conference abstracts
    • Google Scholar
    • Professional organization websites
  1. Pharmaceutical companies
    • Some pharmaceutical companies make their clinical trials available online. Check who the manufacturer is of the drug of interest on the Drugs@FDA website, then check the pharmaceutical company’s website to see if they make their data available.

Sometimes grey literature is needed for a health technology assessment or a health economic evaluation, and fortunately, the Canadian Agency for Drugs and Technologies in Health (CADTH) compiled Grey Matters to recommend sources and to help keep track of which grey literature resources they have searched.

As previously mentioned, searching for grey literature can be a bit tricky, so please do not hesitate to contact the library for help with your grey literature search!


  1. Fourth International Conference on Grey Literature, 1999