A published journal is the entity that defines whether or not its articles are peer reviewed.
Once you find an article that appears to support your response, you should check with the journal to determine if it is peer reviewed or not. These days virtually all journals will have a website.
Lets say that you have articles from 3 periodicals that appear to support your response. They are The Journal of the American Medical Association, Nature, and The New York Times.
If a journal does not state that it is peer-reviewed, it is not. Do not cite or reference sourced without an explicit statement that it is peer-reviewed on the journals website. You will see that both JAMA and Nature are peer-reviewed, but the New Your Times is not.
