This study examines how a substance called **Psilocybin (TRP-8802)**, together with psychotherapy, affects patients with **Irritable Bowel Syndrome (IBS)**. IBS is a condition that causes belly pain and changes in bowel movements. The study involves two groups: one gets immediate treatment, while the other waits 8 weeks. Both groups eventually receive two doses of TRP-8802 and therapy. Researchers will check symptoms like depression, anxiety, and IBS symptoms before and after treatment. **Key Points:** - The study lasts several months, with follow-up visits at 3, 6, and 12 months after treatment. - Participants need to be available for weekly assessments and complete questionnaires. - Safety measures include no tobacco or certain medications before and after treatment. This study is looking for participants aged 21-64, without certain health issues like heart or liver problems. Participants should not use psychoactive substances like alcohol or drugs during the study. It's important to discuss eligibility and participation details with your doctor.