The major difference between a psychiatrist and a psychologist is that the former is a medical doctor while the latter is more of a social scientist. Psychiatrists have MD degrees and are allowed to prescribe drugs. They are concerned at least partially with the physical causes of various mental problems. By contrast, psychologists are only concerned with the mental and emotional bases of mental problems. They cannot do anything for someone who has emotional problems that have a physical basis -- they do counseling and psychoanalysis and such.
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