In the U.S. there is a considerable difference between psychologists and psychiatrists. I was a psychologist, but assuming you're asking about psychiatry, I can explain the main differences. Psychiatry is a specialized field of medicine, and one goes to medical school first and then interns or does a residency in psychiatry. Psychiatrists, being medical professionals, are licensed to prescribe drugs, including psychoactive medications used to treat both major mental disorders (major depression, schizophrenia, psychoses, etc.), and outpatient mental disorders such as depression and anxiety. Sometimes prescription medications are the main or only treatment option available for some disorders. Oftentimes, however, patients or clients with mental disorders receive a combination of medication and various forms of psychotherapy. Psychologists, on the other hand, are not usually authorized to prescribe medications. All of their treatment approaches are "talk therapy" which can include individual, group, couples, family, child, play therapy, among other modalities. Frequently psychologists collaborate with psychiatrists so that the M.D. manages prescription medication while the psychologist provides psychotherapeutic interventions for the same patient. Work schedules depend a lot on work location. If you work in a hospital or medical center you may rotate through some weekends and also have on-call duties. However, psychiatrists and psychologists also can become licensed by a state to engage in independent private practice, where you set your own hours and determine what kinds of clients and treatments to work with.