Serotonin has been implicated in the etiology of many disease states and may be particularly important mental illness, such as depression, anxiety, schizophrenia, sleep disorders, suicide, eating disorders, obsessive compulsive disorders, migraine and others. Many currently used treatments of these disorders are thought to act by modulating serotonergic function. The identification of many serotonin subtypes, most of which have been shown to have functional activity and differential distribution, has stimulated considerable effort into synthesizing selective ligands(drugs) to help understand their significance. This should understand the role of serotonin in mental disorders and these new drugs can be studied alone and in combination with other treatments in order to clarify the parameters of drug use for the clinical effect.