A psychiatrist is a type of medical doctor (physician). To become a psychiatrist, one must attend college, medical school, and then complete at least 4 years of specialized training in psychiatry (5 or 6 years for child psychiatry). Like all other physicians, during medical school, psychiatrists complete rotations in internal medicine, surgery, pediatrics, obstetrics/gynecology, family medicine, neurology, and psychiatry. While applying for residency, medical students decide on a specialty during the fourth year of medical school, and psychiatry is one of many options for them. During residency and fellowship training, psychiatrists learn how to diagnose and treat patients with mental illness using both medication and psychotherapy.
A psychologist is someone who has formal education and training in psychology. Many psychologists become licensed clinicians and work directly with clients, doing therapy or administering psychological tests. Some psychologists have academic positions and choose to do research. Most practicing psychologists are either at the masters or doctoral level.
“Therapist” is a rather general term for a person who does psychotherapy. A psychiatrist or psychologist can serve as a therapist when performing psychotherapy. Social workers often work as therapists, usually at the masters level. In this role, they are often referred to as “clinicians.” Some therapists have specialized training and/or certifications in specific types of therapy (i.e. CBT, DBT, trauma therapy, marriage counseling, family therapy, play therapy, sex therapy, etc.)