Identifying search terms

For any literature search, you will need to identify your search terms.  What words or phrases are you going to search for?   What thesaurus terms are you going to choose?

If you are doing a detailed search for evidence for a systematic review, or doing a systematic search for some other reason, identification of search terms will include identification of synonyms, that is, alternative terms for the concept you are interested in.

Here are some possible ways to identify thesaurus and free text terms, and synonyms. 


Scoping search

Use a PICO grid or similar to identify the search concepts, and search for those.   For example:

Search question: antibiotics to treat otitis media in children under 5.

P - under fives with otitis media
I - antibiotics
C - no stated comparision
O - no stated outcomes

So, search for otitis media and antibiotics, and see what terms are used in titles and abstracts of the articles you find.

Existing strategies

An existing systematic review should include the search strategy used.  Don't feel you have to copy it (of course, if you are doing this exercise for a dissertation, assignment or thesis, you should not and must not copy it!), but it may give you useful terminology.

Background research

Use clues from any background reading you have done about the topic, textbooks, reputable websites, NICE Evidence Search for any clinical topic.

Drug information sources

The British National Formulary is included in NICE Evidence Search, but also try Electronic Medicines Compendium, the European Medicines Agency, and Drugs.com.  Include generic names (long acting insulin) and brand names (glargine), include classes of drugs (antibiotics) and specific types (penicillin).  eMC is a collection of drug information sheets and patient information leaflets.

“Used for” in thesauri 

In a search of Medline, Embase or Cinahl, you must identify relevant thesaurus terms.   Your scoping search will help you - in Ovid or the NHS interface, when you type in a search term, thesaurus terms are suggested to you.  But use the "scope note" and check the "used for" entries.  Articles using those terms in title or abstract will be indexed using the thesaurus term you are looking at.   Therefore, those "used for" entries are useful synonyms to include in your search.

Other people

If you are working on a research project as part of a team, then team members will have suggestions for search terms.   So will patients with that condition, and the team may be able to ask them.  If you are working on an assignment, dissertation or thesis, you may be on your own (although if you have a supervisor, ask if they can advise you).   It is worth talking to others, and checking that you understand the search keywords in the same way as them, and that you know what they mean. 

Known items

You looked at titles and abstracts of items that appeared in the results of your scoping search.  But have a look at the titles and abstracts, and full text, of items that you know about already, and items you find in your actual search.   And look at the titles of references in the bibliographies of relevant items.

MeSH on Demand

This is a National Library of Medicine service, which identifies MeSH terms in text that you enter.  I have not yet tried this, but it seems to have possibilities.  I have written a separate post about this.