Information and research conducted by the federal government and international non-governmental organizations can be vital to your work, and is also usually free to read.
Use a government portal to find information on a topic by every relevant agency, or go directly to the federal departments that focus on biomedical research.
Search across government agencies.
Sources considered gray — data collected by a federal agency, or a technical report by a professional association, for example — are certainly edited in some way but do not go through peer review, so while they are published documents, they are not considered scholarly articles.