• Serum cortisol / ACTH and DHEA levels [ Time Frame: taken at 20 minute intervals over the study period. ]
  

• Serum cytokine levels [ Time Frame: taken at 20 minute intervals over the study period. ]
  

Inclusion Criteria:

• Has IBS as defined by the Rome II criteria.
• Clinical laboratory tests at screening showing no clinically significant abnormalities in the opinion of the Principal Investigator.
• Non-tobacco user (abstinence from tobacco use for at least 1 month before the start of the study).

Exclusion Criteria:

• As a result of any of the medical interview, physical examination, evaluation of mental state and psychiatric history or screening investigations the physician responsible considers the subject unfit for the study.
• Subject has any of the following exclusionary psychiatric conditions (Note: current diagnoses are to be based on the M.I.N.I administered at screening).
• 1. A current DSM-IV Axis I disorder such as Dysthymia, Phobia, Major Depression, Obsessive Compulsive Disorder, Body Dysmorphic disorder, or Panic Disorder as a primary diagnosis currently or within 6 months prior to the screening visit.
• 2. A current DSM-IV-TR diagnosis of Antisocial or Borderline Personality Disorder, Dementia, or another current DSM-IV-TR Axis II diagnosis that would suggest non-responsiveness to pharmacotherapy or non-compliance with the protocol; or
• 3. A current (within six months prior to Screening Visit) diagnosis of anorexia nervosa or bulimia; or
• 4. A history of Schizophrenia, Schizoaffective Disorder, or a Bipolar Disorder; or
• 5. Is currently being treated by medication for any of the above psychiatric disorders. Psychiatric medications would include, but not limited to, antidepressants (e.g. SSRIs, SNRIs, TCAs) anxiolytics, antipsychotics
• Subjects who, in the investigator's judgement, pose a current, serious or suicidal or homicidal risk or have made a suicide attempt within the past 6 months or have ever been homicidal.
• subjects who have taken any medication for the treatment of IBS within 1 month prior to screening except for anti-diarrhoeal medications or laxatives for control of bowel habit which is allowed if at a stable dose for 2 weeks prior to randomisation.
• Subjects who are taking NSAIDs including aspirin on a regular basis or within 48 hours of a study day.
• Subjects with a history of PUD <10 years ago.
• The subject has a history of, or active eating disorder.