Other drugs much more potently activate brain reward systems. Initial use of these substances is usually accompanied by mood elevation and other affective changes that lead to their recreational use. Much like moderate caffeine and alcohol use, addictive drugs activate brain reward systems. But the activation is much more intense causing the individual to crave the drug and to focus their activities around taking the drug. The ability of addictive drugs to strongly activate brain reward mechanisms and their ability to chemically alter the normal functioning of these systems can produce an addiction.
Many drugs interact with brain mechanisms involved in affect, cognition, and behavior.
These compounds are termed psychoactive drugs. Drugs are usually classified according to their primary therapeutic actions. Antipsychotic drugs are used to treat schizophrenia and produce a normalization of the disordered thought processes associated with this illness. Antidepressant drugs are used to treat psychological depression and produce a normalization of disturbed affective states characteristic of depression. These and numerous other drugs have important clinical uses and have revolutionized the treatment of many mild to severe mental disorders.