Psychology is the scientific study of behavior and mental processes while psychiatry is a branch of medicine. Psychiatrists are medical doctors who provide both medical and psychological therapy treatments.Psychologists can counsel patients, as can psychiatrists, but only psychiatrists can prescribe medicinal drugs and therapy treatments.sychiatrists are medical doctors who provide both medical and psychological therapy treatments. Psychologists can counsel patients, as can psychiatrists, but only psychiatrists can prescribe medicinal drugs and therapy treatments.