Note that psychiatry is practiced by psychiatrists, psychology by psychologists. Psychiatrists have medical training, while psychologists do not (but sometimes have extremely extensive training in therapy).
Psychiatry was at first a pragmatic discipline that was part of general medicine, combining medicine and practical psychology. The work of Emil Kraepelin laid the foundations of scientific psychiatry, but was derailed by the psychoanalytic theories of Sigmund Freud. For many years, Freudian theories dominated psychiatric thinking.
The discovery of lithium carbonate as a treatment for bipolar disorder, followed by the development of fields such as molecular biology and tools such as brain imaging[?] has led to psychiatry re-discovering its origins in physical and observational medicine without losing sight of its humane dimension.
Unlike most other areas of medicine, there is a politicised anti-psychiatry movement that opposes the practices of, and in some cases the existence of, psychiatry. Some opponents of psychiatry state that selective financing by large multinational drug companies of both high ranking professional psychiatrists, research and educational material has lead the practice of psychiatry to be subversively, and in some cases inhumanely misled.