Peer-reviewed journals do contain some information that is itself not refereed, such as editorials, opinions, letters, and book reviews. So, you need to consider whether the individual article or essay has been reviewed and approved by other scholars.
Many databases have an option for limiting to peer-reviewed journals. Check the limit options on the advanced search screen of a database to see if you can limit your search to articles that have been published in peer-reviewed journals.
Look for options such as