Two Important Notes
Most article databases now have a limiter located below the search box that can be check marked to limit search returns to peer reviewed journals:
Not all articles appearing in journals labeled peer reviewed actually go through the peer review process. Some articles that appear in peer-reviewed journals, such as news items, editorials, and book reviews, do not have to go through a review process. Those types of articles would not be considered peer reviewed though they appear when you limit to journals labeled peer reviewed.