While substance use and other neuropsychiatric disorders such as schizophrenia and mood disorders are chronic disorders, the presence of a therapeutic or abused substance component may produce dynamic changes in the expression of specific genes. From the temporal changes in gene expression in animal experiments35–36 and from imaging studies of the metabolic responses of the addicted brain to drugs37–39, these changes appear to depend on the nature and manner in which drug(s) are used.
