A psychiatrist has an MD degree (Doctor of Medicine) or DO (Doctor of Osteopathy) and has chosen to specialize in the branch of medicine that focuses on mental health issues. A psychiatrist treats patients by talking with them as well as by prescribing medication (if needed). Psychologists have one of these degrees: PhD (Doctor of Philosophy), PsyD (Doctor of Psychology), or EdD (Doctor of Education). A psychologist treats patients by talking with them but does not prescribe medication.