Each database has usually its own thesaurus or keyword list
In PubMed you have MESH terms and subheadings, in Embase Emtree thesaurus and in PsycInfo its own thesaurus. One of the advantages of using thesaurus terms in the search is that you can usually explode the terms and search also subterms (narrower terms) with one search command.
The structures of thesauri differ from one datatabase to another. For example the MeSH (Medical Subject Heading) term Occupational health has no subterms in MEDLINE but the Emtree term Occupational health has about 20 subterms in Embase. Thus it is important to build a unique strategy for each database.
Here we list search filters for identifying randomised trials in PubMed, Embase and PsychINFO. In CENTRAL you need not use an RCT filter because all the records are thoroughly and correctly indexed. This means you can just limit your search to study type. The filter for PubMed is straight from the Cochrane Handbook and the other two have been published elsewhere and have been tweaked by us.