Many medical databases have an official, highly structured set of subject headings - also known as a thesaurus - which are used to describe the content of journal articles.

The best known of these thesauri is MeSH - Medical Subject Headings: this is used in MEDLINE and PubMed, and other databases including the Cochrane Library.

CINAHL has its own set of subject headings - CINAHL Headings.

In the health sciences, a search using the thesaurus is probably the best type of search you can do. But it's important to check what the subject headings are. Some databases, including CINAHL and MEDLINE, make this easier for you by offering a "Suggest subject terms" (CINAHL) or a "Map term to subject heading" (MEDLINE) feature. PubMed automatically "maps" your search terms to MeSH terms, as well as searching for them as keywords.

If you do search using CINAHL Headings or MeSH terms, you sometimes have to do this by one search idea at a time, and combine the search sets later using your Search History.