Psychopharmacology is defined as the use of drugs to modify mental or behavioral performance. In general, psychopharmacology is used in the treatment of biologically based mental illnesses, although there has been increased interest in using drugs to enhance performance in healthy individuals.

Psychopharmacology assumes a strong mind-brain connection, if not a complete reduction of mind to brain. However, early theories about the relationship of brain chemistry to behavior were weak and post hoc. Most drugs were discovered accidentally and adopted because of their effects on symptoms (Valenstein 1998). Only later were theories of the ways drugs act on the brain developed, followed by theories of how mental states are related to brain chemistry. Although the mechanism of action on neuronal receptors has been elucidated for many drugs, the mechanisms by which drugs influence behavior at the whole-brain level are poorly understood. There are no definitive biological markers for diagnosing...