About Grey Matters


CADTH — the Canadian Agency for Drugs and Technologies in Health — provides Canada’s federal, provincial, and territorial health care decision-makers with objective evidence to help make informed decisions about the optimal use of drugs and medical devices in our health care system. To achieve its mandate, CADTH produces a variety of publications that range from comprehensive systematic reviews and economic evaluations to more concise bulletins and updates.

To search for and retrieve the evidence base required to produce CADTH reports, CADTH’s Research Information Services team has developed and made available a grey literature resource, the CADTH Grey Matters tool. Grey literature includes government information and reports that are not published commercially and that may be inaccessible via bibliographic databases. This tool is used to:

  • ensure the retrieval of relevant health technology assessment (HTA), government, and evidence-based reports that may not be indexed in bibliographic databases such as MEDLINE;
  • document the grey literature search process, thereby increasing transparency and the potential for reproducibility; and
  • ensure that grey literature searching is done in a comprehensive way, according to international standards.1-2


This tool is intended for use by librarians; information specialists; and researchers who are producing systematic reviews, HTAs, drug assessments, or economic evaluations.


CADTH Grey Matters resource is not exhaustive, but it does strive to be comprehensive regarding Canadian and international HTA agencies. The main categories within this tool are: Health Technology Assessment (HTA) Agencies, Health Economics, Clinical Practice Guidelines, Regulatory Approvals, Advisories and Warnings, Drug Class Reviews, Clinical Trials Registries, Canadian Drug formularies, Canadian Physician Fee Schedules, Databases, and Health Statistics. To compensate for the focused characteristics of the resource, supplemental keyword searches on search engines such as Google are recommended.

The Grey Matters tool is updated regularly to ensure the website links and search tips are accurate, and to incorporate new sources. However, because of the continuously evolving nature of the internet, CADTH cannot be held responsible for occasional inaccuracies due to website changes.

How To Use This Resource

This tool is organized by category. It includes tips on navigating the websites. Although the websites are usually assigned to only one category, in many cases an individual website may have relevancy in additional categories.

The Grey Matters tool is meant to be used to document all aspects of the search process. This includes the documentation of the keywords used in the search, and information about the availability of each website. Each record listed in the Grey Matters tool has a notes field that can be used to document the search terms used on the individual websites listed or to make other notes.

Selective or targeted searching by category may be required, and time spent will vary according to the needs of a particular project. A 2014 study highlighted that the average time spent searching grey literature for systematic reviews as being roughly a quarter of overall searching time.3 It is not mandatory to search every website on this checklist in order to conduct a comprehensive grey literature search.

How to Save and Print Selected Records

  • To print selected categories or records, click on the Print/Copy icon. Print / Copy
  • To save selected categories or records into a Word file, click on the Print/Copy icon, select all of the text, copy the selected text, paste it to a Word file, and click Save.
  • The URL links will be active.
  • To save selected categories or records as a PDF file, click on the PDF icon. PDF

How to Cite this Resource

Grey Matters is an open access tool and may be used for non-commercial purposes, provided that attribution is given to CADTH.

Cite as: Grey matters: A tool for searching health-related grey literature. Ottawa: CADTH; 2022: https://greymatters.cadth.ca. Accessed yyyy-mm-dd.

CADTH Searching Tools and Resources

A shortlist of the Grey Matters tool has also been produced, entitled Grey Matters Lite. This shortlist includes key resources from the following sections of the Grey Matters tool: Health Technology Assessment (HTA) Agencies, Clinical Practice Guidelines, Regulatory Approvals, Advisories and Warnings, and Clinical Trial Registries. Grey Matters Lite is available under the Other Resources tab. A variety of other literature searching tools and resources provided by CADTH Research Information Services are available at Finding the Evidence: Literature Searching Tools in Support of Systematic Reviews .


1. Higgins JPT, Green S, eds.  Cochrane handbook for systematic reviews of interventions . Version 5.1.0. [Updated March 2011]. The Cochrane Collaboration; 2011.

2. Higgins JPT, Lasserson T, Chandler J, Tovey D, Churchill R. Standards for the conduct of new Cochrane Intervention Reviews . In: Higgins JPT, Lasserson T, Chandler J, Tovey D, Churchill R. Methodological Expectations of Cochrane Intervention Reviews . Cochrane: London, 2016. See Searching for studies.

3. Saleh A, Ratajeski M, Bertolet M. Grey literature searching for health sciences systematic reviews: a prospective study of time spent and resources utilized . Evidence Based Library and Information Practice 2014;9(3):28-50.