Below is an exhaustive list of grey literature sources or unpublished, non-peer reviewed sources that are commonly searched in systematic reviews to combat publication bias. This list was started in 2025 by Melis Lydston, MLS, and is licensed under CC BY-NC-ND 4.0.

Aggregate Grey Literature Databases

• Center for Research Libraries: Provides free access for member libraries
• GreyNet’s PubGrey (This isn’t a database per se*,* but it lists producers of grey literature in case you want to track those down on your own.)
• OAIster
• OpenGrey: Click the DANS Easy Archive link. You’ll see a few prompts, then you can select your academic field.
• Policy Commons: Offers a “freemium” version where you can perform 25 searches a month after signing up for a free account.

Clinical Trials

• CenterWatch
• EU Clinical Trials Register
• WHO International Clinical Trials Registry Platform (ICTRP)

Country-Specific

• ClinicalTrials.gov (US)
• ReBEC trial registry (Brazil)
• Health Canada trial registry
• ChiCTR trial registry (China)
• ITMCTR trial registry (China, traditional medicines)
• AUO trial registry (Germany, urological oncological studies)
• HKUCTR trial registry (Hong Kong)