PRN is a Latin medical term that means "as needed." It is often used by physicians to indicate a medication or treatment that should be administered only when necessary. While PRN is a common abbreviation in medical settings, it is not the only term used to express this idea. Some synonyms for PRN include "as required," "as necessary," "when called for," "as the occasion arises," and "whenever needed." These terms all convey the same basic idea as PRN, that a medication or treatment should be used only when the patient needs it. Healthcare professionals must be familiar with all of these terms to ensure that they provide the best care to their patients.