The purpose of this study is to evaluate the effect of varenicline on rectal sensation, based on ascending method of limits and on graded rapid phasic distensions in participants with non-constipation IBS and chronic abdominal pain.

Inclusion Criteria:

1. Participants will be 18-70 years of age
2. Irritable bowel syndrome with pain, but no constipation [that is IBS-D (diarrhea), IBS-M (mixed), or IBS-U (unspecified)]

Exclusion Criteria:

1. Diagnosis of moderate-severe depression as per HADS>8
2. Alcohol or illicit substance dependence or abuse in the past 12 months
3. Dementia, unprovoked seizure history, seizure disorder
4. Pregnancy (all women of childbearing potential will be required to have a negative pregnancy test prior to initiation, and will be on a highly effective method of contraception, as detailed in the consent form)
5. Significant change or increase in antidepressant or pain medications within the last four weeks; significant change in primary treatment interventions for pain in the past four weeks
6. Medically unstable
7. Severe hepatic or renal impairment, such as baseline AST or ALT >2.5 X upper normal limit or end-stage renal disease with estimated glomerular filtration rate or creatinine clearance <15 mL/min
8. Concomitant use of strong CYP3A4 inhibitors and strong or moderate CYP3A4 inducers

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 12/27/2024. Questions regarding updates should be directed to the study team contact.