There is no way to limit search results on the PubMed service to peer-reviewed articles as of 2015. The U.S. National Library of Medicine that maintains the PubMed service does not keep a list of peer-reviewed journals, though the majority of indexed journals and articles are peer-reviewed or refereed.
PubMed is a free index of the NLM's Medline database of medical and health care-related science article abstracts and citations, updated daily with new citations. While it offers an advanced search feature and the ability to filter results, none of the entries are marked by peer-review status. Because there are a number of different qualifications and criteria for peer reviews, the NLM does not record this information in the database.
To determine whether an article is peer-reviewed or refereed, check with the publisher or the editorial information for the specific journal that published the article in question. Another option is to find a directory online or in print of peer-reviewed journals. The EurekAlert! service run by the American Association for the Advancement of Science maintains an online list of peer-reviewed journals, and the downloadable title lists on Ebsco's research databases site indicate whether each journal included meets Ebsco's guidelines for being considered peer-reviewed.