A Placebo-Controlled Trial of St. John's Wort for Irritable Bowel Syndrome

Inclusion Criteria: * Established diagnosis of IBS * Meet Rome II diagnostic criteria for IBS * 18-70 years of age * U.S. resident * English-speaking (able to provide consent and complete questionnaires) * Able to participate in all aspects of the study Exclusion Criteria: * Known alternative/concurrent gastrointestinal diagnosis (e.g. Crohn's disease, ulcerative colitis, microscopic colitis, celiac sprue, chronic pancreatitis or pancreatic insufficiency, scleroderma, chronic intestinal pseudo-obstruction, bacterial overgrowth, recent (\<6 months) intestinal bacterial/protozoal/ parasitic infections, HIV, fecal incontinence, small bowel or colonic resection, pelvic floor dysfunction, paraplegia or quadriplegia) * Current symptoms of severe depression, as measured by Center for Epidemiological Studies Depression Scale (CES-D) score * Mental retardation or any condition requiring a legal guardian * Current or past history of psychotic disorder (schizophrenia, bipolar disorder) * Recent or current use (within past 30 days) of select mood or pain or symptom-altering medications: * benzodiazepine use * substance abuse * narcotic use * antihistamine use * barbiturates * zaleplon (Sonata) * Recent or current use (within past 30 days) of drugs that interact with SJW: * antidepressants or antipsychotics * tramadol (Ultram) * sumatriptan (Imitrex) * digoxin (Lanoxin) * anticonvulsants (e.g. carbamazepine or phenytoin) * immunosuppressants: cyclosporine and tacrolimus * HIV protease inhibitors (e.g. indinavir), non-nucleoside reverse transcriptase inhibitors (e.g. nevirapine) * warfarin (Coumadin) * theophylline * chemotherapy * sulfa-containing drugs * piroxicam (Feldene) * simvastatin (Zocor) * sibutramine (Meridia) * verapamil (Calan or Isoptin) * Planned surgery (especially transplant) or anesthesia exposure during trial * Known photosensitivity or planned photodiagnostic or phototherapy procedures * Are pregnant, lactating, likely to become pregnant during medication phase and not willing to use a reliable form of contraception (barrier contraceptives, diaphragm, injections, intrauterine device, surgical sterilization, and abstinence) * Recent or current use (within 30 days) of SJW, other herbal products for IBS, investigational drug use * Known allergy to SJW * Significant acute or chronic progressive neurologic, hepatic, renal, cardiovascular, respiratory or metabolic disease * Recent history of alcohol or substance dependence use or abuse * Another household member or relative participating in the study * Professional drivers or operators of heavy machinery * Major cardiovascular events in the last 6 months * Use of IBS-specific drugs such as tegaserod (Zelnorm) and Lotronex (Alosetron) (within 30 days)