The prevalence rate of IBS in 1998 in the U.S. was approximately 5,700 cases per 100,000 persons, with a much higher rate in Caucasians than in Hispanics or Afro-Americans. The total direct cost of IBS, including costs of inpatient and outpatient health services utilization and prescription medication, was greater than $1.6 billion annually in 1998 in the U.S., while the indirect costs, primarily absenteeism from work, are estimated at over $20 billion. (1 AGA: The burden of gastrointestinal diseases) IBS is treated primarily in the physician's office, with patient education, assurance and/or dietary and lifestyle modifications being the rule for mild cases, but prescription medicines being offered in more moderate cases. Prescription therapy for theses patients generally falls under two categories - drugs affecting gut physiology and psychological treatment. Very severe cases may be treated by centrally-acting agents (i.e., tricyclic antidepressants [TCAs] or selective serotonin reuptake inhibitors) together with psychological methods.