Table 2. Databases' main characteristics.

Principal databases where the main articles of the whole body of the research can be gathered. This is an example of specialities and it can be used for the researchers to have a variety of databases to work.

NLM, National Library of Medicine; ICTRP, International Clinical Trials Registry Platform; LILACS, Literatura Latino-Americana e do Caribe em Ciências da Saúde

Database	Principal characteristics
PubMed [12,13]	A free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. It is maintained by the United States NLM at the National Institutes of Health
EMBASE [14]	A biomedical and pharmacological database containing bibliographic records with citations, abstracts, and indexing derived from biomedical articles in peer-reviewed journals. It is especially strong in its coverage of drug and pharmaceutical research.
Cochrane [15]	A database of systematic reviews. It includes reliable evidence from Cochrane and other systematic reviews of clinical trials
Google Scholar [16]	A freely accessible web search engine that indexes the full text or metadata of scholarly literature across an array of publishing formats and disciplines.
Web of Science [17]	A research database used for citation analysis. It provides access to multiple databases including the Science Citation Index, the Social Sciences Citation Index, and the Arts and Humanities Citation Index.
Science Direct  [18]	A full-text scientific database offering journal articles and book chapters from more than 2,500 peer-reviewed journals and more than 11,000 books.
PsychINFO [15]	An electronic bibliographic database providing abstracts and citations to the scholarly literature in the psychological, social, behavioral, and health sciences.
ICTRP [19]	ICTRP is a database of clinical trials being conducted around the world. It is maintained by the World Health Organization.
Clinical Trials [20]	A database of privately and publicly funded clinical studies conducted around the world. It is provided by the United States NLM.
LILACS [21]	The LILACS is an online bibliographic database of scientific and medical publications maintained by the Latin American and Caribbean Center on Health Sciences Information.