Answer
In EBSCOhost databases, such as Academic Search Ultimate, you'll see Refine Results in the left sidebar of your search results. Under Limit To there is checkbox to limit to Peer Reviewed.
For the most part, this filtering will be correct, but sometimes it's only the journal that is peer reviewed, while a particular article may not be. In the individual sources, watch for phrases like "Opinion" at the top of the page or a lack of cited sources in the article. In the individual source result page, there will be details listing whether the source is peer reviewed or not.
To verify whether a journal is peer reviewed, you can search for the journal's title at Ulrichsweb. Look for the icon that says Refereed.
For more information on peer reviewed sources, see our Finding Peer Reviewed Articles guide or contact a librarian.