Once you have a reasonably well defined research question, it is important to make sure your project has not already been recently and successfully undertaken. This means it’s important to find out if there are other research syntheses (including systematic reviews) that have been published or that are in the process of being published on your topic.
If you are submitting your systematic review for funding, for example, you may want to make a good case that your review or synthesis is needed and not duplicating work that has already been successfully and recently completed—or that is in the process of being completed. It is also important to note that what is considered “recent” will depend on your discipline and the topic.
Even if you do find another review or synthesis on your topic, it may be sufficiently out of date or you may find other defendable reasons to perform it again. In addition, looking at other research syntheses published around your topic may also help you refocus your question or redirect your research toward other gaps in the literature.
These tips may not cover every possible type of research synthesis but they provide a decent start.
Search databases specifically focused on systematic reviews using a very broad search strategy, databases such as:
The Cochrane Library (including systematic reviews of interventions, diagnostic studies, prognostic studies, and more) is an excellent place to start.
By default, the Cochrane Library will display “Cochrane Reviews” (Cochrane Database of Systematic Reviews, aka CDSR). You can ignore the results which show up in the Trials tab when looking for systematic reviews: They are records of controlled trials relevant to Cochrane reviews. There is also an option to see "Other Reviews" under "More". "Other Reviews" are results from Epistemonikos.
The example shows the number of Cochrane Reviews with hiv AND circumcision in the title, abstract, or keywords.
In addition, you can perform a sufficiently developed search strategy on MEDLINE via PubMed (be as broad in your search as is reasonable) and then use the “Article types” filter for “Systematic Reviews” to see if other reviews have been published on your topic. Systematic reviews found in PubMed and not included in The Cochrane Library may require more careful critical appraisal for quality assessment.
See Systematic Reviews Search Strategy Applied in PubMed for details.
Alternative interface to PubMed: You can also search MEDLINE on the Ovid platform. Perform a sufficiently developed search strategy (be as broad in your search as is reasonably possible) and then choose the journal subset for Systematic Reviews Pre 2019 (more sensitive, less accurate -- it is, in fact, a search filter, and not a publication checktag/limit; because it is not a checktag/limit, it is not as accurate) or Systematic Reviews.
Once you have run your search, to limit to systematic reviews: Go to Additional Limits, and under EBM-Evidence Based Medicine, choose Systematic Review
Other approaches: To search for systematic reviews in Embase on Ovid, perform a reasonably developed search strategy (be as broad in your search as is reasonably possible) and then combine your search results with a systematic review filter developed for Embase on Ovid, e.g., filters available at https://sites.google.com/a/york.ac.uk/issg-search-filters-resource/filters-to-identify-systematic-reviews
Example of a filter used to find systematic reviews for BMJ Clinical Evidence (can be copied and pasted into the Embase search box then combined with the concepts of your research question):
(exp review/ or (literature adj3 review$).ti,ab. or exp meta analysis/ or exp "Systematic Review"/) and ((medline or medlars or embase or pubmed or cinahl or amed or psychlit or psyclit or psychinfo or psycinfo or scisearch or cochrane).ti,ab. or RETRACTED ARTICLE/) or (systematic$ adj2 (review$ or overview)).ti,ab. or (meta?anal$ or meta anal$ or meta-anal$ or metaanal$ or metanal$).ti,ab.