In 2020, the National Library of Medicine (NLM) launched the NIH Preprint Pilot to test the feasibility of making NIH-funded preprints discoverable in PubMed Central (PMC) and by extension, PubMed. Preprints are complete, public drafts of articles that have not yet been peer reviewed. Phase 1 sought to answer the NLM's question: do preprints in PMC accelerate the discoverability and maximize the impact of NIH-supported research? This first phase of the pilot focused on archiving preprints reporting SARS-CoV-2 virus/COVID-19 research and resulted in more than 3,500 preprints being added to the NLM database, accelerating access to NIH-supported research results by an average of more than 100 days (see Funk et al., 2022).
NLM announced Phase 2 of the NIH Preprint Pilot in late January. Running for one year, this phase expands the inclusion of preprints across NIH-funded research, removing the limit to COVID-19 research. Preprints that acknowledge direct NIH support or have an NIH-affiliated author and are posted to an approved preprint server (ie., bioRxiv, medRxiv, arXiv, or Research Square), will be added to PMC and receive a corresponding citation in PubMed.
It is important to NLM that researchers, clinicians, and the public can easily distinguish between preprints and peer-reviewed journals articles, so PMC and PubMed prominently flag preprint articles with a green label.
While NIH encourages preprints to be cited where other research products are cited ((NIH Biosketch, Research Performance Progress Reports, and grant applications), they do not fall under the NIH Public Access Policy, as they are not peer-reviewed. See this video on how to add preprint citations to My Bibliography,