[1] Since 1879, the National Library of Medicine has published Index Medicus, a monthly guide to medical articles in thousands of journals.
MEDLARS cost $3 million to develop, and at the time of its completion in 1964, no other publicly available, fully operational electronic storage and retrieval system of its magnitude existed.
[5] This early system covered 239 journals and boasted that it could support as many as 25 simultaneous online users (remotely logged in from distant medical libraries) at one time.
[6] However, this system remained primarily in the hands of libraries, with researchers able to submit pre-programmed search tasks to librarians and obtain results on printouts, but rarely able to interact with the NLM computer output in real-time.
In 1996, soon after most home computers began automatically bundling efficient web browsers, a free public version of MEDLINE was deployed.
This system, called PubMed, was offered to the general online user in June 1997, when MEDLINE searches via the Web were demonstrated.
[6] In December 2024, the database contained more than 38 million records[7] from over 5,200 selected publications[8] covering biomedicine and health from 1781 to the present.
Being an aggregated source, the PubMed database suffers from multi-source problems such as inconsistent representations from the upstream data providers.
Engines designed to search MEDLINE (such as Entrez and PubMed) generally use a Boolean expression combining MeSH terms, words in the abstract and title of the article, author names, date of publication, etc.
[10] MEDLINE added a "publication type" term for "randomized controlled trial" in 1991 and a MESH subset "systematic review" in 2001.