Psychiatrists are medical doctors who specialize in the diagnosis and treatment of mental illness and substance abuse disorders. Psychiatrists differ from psychologists in that they have completed their training to become an MD, and can prescribe medications.

Psychiatry seeks to understand both the physical functioning of the body, and the complex linkage between mental and physical illnesses. In many cases, testing is necessary to rule out physical causes before emotional or mental causes may be considered.

Psychiatrists may order diagnostic physical and mental tests, prescribe medications and practice psychotherapy in the course of treatment. They often consult with or are referred by primary care physicians and psychotherapists.