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Gerstein Science Information Centre

Searching the Literature: A Guide to Comprehensive Searching in the Health Sciences

Students and researchers in the health sciences are often required to conduct comprehensive searches of the literature. Follow the steps in this guide to learn how this process works.

What are search filters?

Search filters are:

  • also known as hedges
  • pre-cooked search strings that are designed to limit search results
  • designed to be highly-sensitive, precise, or a balance of both

Commonly, search filters limit search results by:

  • age group
  • publication type
  • study design

They are sometimes available at the click of a button in library databases, but don't let that deceive you! A lot of work goes into developing an effective search strategy for filters, and they often include various combinations of subject headings, textwords, and wildcards.

NOTE: Use filters with caution! 
Many search filters are interface-specific and only available for certain databases.  Some filters have been validated; many have not. 


Resources for Search Filters

RCT & Human Filter - Medline

PubMed - Randomized Controlled Trials 

From the Cochrane Handbook, Section 6.4.11, Box 6.4.a:

(((((((((randomized controlled trial [pt]) OR controlled clinical trial [pt]) OR randomized [tiab]) OR placebo [tiab]) OR drug therapy [sh]) OR randomly [tiab]) OR trial [tiab]) OR groups [tiab])) NOT ((animals [mh] NOT humans [mh])) 

From Glanville, J. M., Lefebvre, C., Miles, J. N. V., & Camosso-Stefinovic, J. (2006). How to identify randomized controlled trials in MEDLINE: ten years on. Journal of the Medical Library Association94(2), 130–136.:

(((((((clinical trial[pt]) OR randomized[tiab]) OR placebo[tiab]) OR clinical trials[mh]) OR randomly[tiab]) OR trial[ti])) NOT ((animals[mh]) NOT (animals[mh] AND humans[mh])) 

OVID Medline - Randomized Controlled Trials

From the Cochrane Handbook, Section 6.4.11, Box 6.4.a:












randomized controlled

controlled clinical



drug therapy.fs.




1 or 2 or 3 or 4 or 5 or 6 or 7 or 8

exp animals/ not

9 not 10