It is important to search two to five databases individually. Only searching one database or using the Library's MegaSearch is not acceptable. Which databases and how many you choose to search depends on the topic of the systematic review.
The Cochrane Collaboration considers these bibliographic databases as the most important sources for reports of trials (Cochrane Handbook, 184.108.40.206):
National, regional and subject-specific databases should be selected for searching according to the topic of the review (Cochrane Handbook, 220.127.116.11). Other subject-specific and citation databases include:
TIP! Register with each database so you can: save your search history, create alerts, re-run a search, print a record of your search
A new study suggests that for biomedical systematic reviews these four databases should be searched (listed in order of importance):
Other databases such as CINAHL or PsychINFO should be added if the focus of the review is on nursing/allied health or psychology, respectively.
Bramer, WM, Rethlefsen, ML, Kleijnen, J & Franco, OH 2017, 'Optimal database combinations for literature searches in systematic reviews: A prospective exploratory study', Systematic Reviews, vol. 6, no. 1, p. 245.