A physician assistant is a licensed health care professional who works under the supervision of M.D. or D.O. to perform many of the tasks that were once carried out solely by doctors. Physician assistants can perform physical exams, diagnose and treat illnesses, order and interpret tests, counsel patients on preventative health care, assist in surgery, and in most states, even write prescriptions. As a student you can expect to spend 27 months training both in the clinic and in the classroom once you’ve completed your undergraduate degree.