Tip #71: Removing Clinical Trials Records from Embase.com and Cochrane CENTRAL

A huge thanks to John Reynolds, MLIS, from the Louis Calder Memorial Library at the University of Miami Miller School of Medicine, who wrote this post!

Embase (Elsevier’s Embase.com) has recently added large numbers of clinical trials records to their database and includes them in search results by default. Starting in May 2025 they added 500,000 records from ClinicalTrials.gov and continue to add new records. See their FAQ for more information.

Similarly, Cochrane CENTRAL (Wiley) has been adding clinical trials registry records from ClinicalTrials.org and the WHO ICTRP since 2023. It also contains registry records identified through its own Specialized Registers and Handsearch projects. See this FAQ on how trials records are added.

While trials records can be useful for many kinds of research, many people may not want trials records in their search results, or may prefer to search trials registries directly. While both Embase and CENTRAL allow searchers to identify and limit search results to trials registry records, neither has a built-in filter to exclude them from search results.

Fortunately, removing them from a set of results is simple.

Removing clinical trial records in Embase.com:

In Embase.com, you can add #X NOT 'clinical trial'/it, where X is your last search line number; it is the field code for publication type.

If, like me, you cannot remember whether to use the singular trial or the plural trials, exactly where the punctuation goes, or what it stands for, you have an easy workaround in the filter panel. Expand Publication Types, check the Clinical Trial box, and click the Apply button.

This runs a search #X AND 'clinical trial'/it. In the search box, replace AND with NOT, run the search, and clinical trials records will be removed from your results. You can use this same technique to remove preprints or any other publication type, too.

Removing clinical trial records in Cochrane CENTRAL on the Wiley platform:

In Cochrane CENTRAL, if you use the Search Manager in the Advanced search mode, it’s easy to view just ClinicalTrials.gov and/or WHO ICTRP trials records, but not to remove them from your results.

I developed a workaround to exclude these records after considerable trial and error and refinement over time. You may want to keep this little hedge handy, since there does not seem to be a way to get there from the search history:

#X NOT ((trial registry record):pt OR (Ictrp OR ctgov):an OR (trialsearch OR clinicaltrials):so) where X is the last line of your search strategy.

Trial registry origin can be found in the Accession Number field, AN, which can be searched by the source database or accession number ID; the Source field, SO; and publication type, PT. Unfortunately, not all trials records have accession numbers, so using AN alone can result in missed records. There are also many sources for trials in CENTRAL beyond ClinicalTrials.gov and ICTRP, such as records from the trials registers of individual countries, from pharmaceutical companies, and from individual journals. Also, some records that are clearly from trials registries, such as ClinicalTrials.gov, are tagged as journal articles. A hedge that searches all three fields seems to be the best way to remove as many trials registry records as possible, leaving only actual reports on trials with results.

Below is an illustration of how each of the fields retrieves a trials record.

For more details about clinical trial records in Cochrane CENTRAL, see the Cochrane Library User Guide, the Cochrane Search Manager Help Page, the How CENTRAL is Created page, and the Cochrane Library Field Guide.