All assessments and patient interactions have been designed with COVID-19 uncertainties in mind: the investigators can maintain social distancing and use masks during the two in-person visits, and much of the study, including the follow-up session, is conducted remotely.

Baseline Screening and Assessment. Each participant will come to the Health and Human Performance laboratory at CMU for a baseline assessment appointment. They will be apprised of the study aims and approach, provide written informed consent, and complete a brief in-person screening evaluation for study eligibility. Eligible participants will complete a baseline survey assessment (including measures such as IBS illness severity, IBS quality of life, demographics and health measures) and learn how to complete the EMA assessments on data-enabled smartphones. The EMA smartphone assessments will consist of three types of momentary experience data over a period of seven consecutive days following the baseline appointment: (1) participants will be quasi-randomly sampled 3 times per day during waking hours to assess stress and IBS symptoms; (2) participants will be asked to complete event-driven momentary assessments of distress and IBS symptoms after bowel movements; and (3) participants will be asked to complete a daily diary assessment to assess IBS symptoms, IBS distress, and mood throughout the day. The investigators will implement an easy-to-use smartphone-enabled EMA sampling program that is downloaded onto each of the phones provided to participants for the duration of the study. Participants will be instructed to complete each EMA assessment as soon as they are beeped. Additionally, participants will be given instructions on how to provide a baseline stool sample for microbiome analysis.

Intervention. Participants will be randomized to either MA-MBI, MO-MBI, or Coping Control (CC) using a 2:2:1 randomization sequence (i.e., for every five individuals randomized, 1 will be assigned to CC). Participants will remain blind to the type of intervention program they are receiving until post-study debriefing, to minimize potential expectancies. The MA-MBI program is a Mindfulness-Based Intervention (MBI). The instructed meditation techniques enable participants to (a) monitor their present-moment body experience while (b) accepting each experience. The MO-MBI program is structurally matched to the MA-MBI program, with no instruction on acceptance. The program instructs participants to concentrate on and (a) monitor physical and emotional body experience during each meditation practice. The Coping Control (CC) program, also matched to the MBI programs, includes no monitoring or acceptance instruction and instead focuses on coping effectiveness strategies. Participants are instructed in 3 skills: (a) thoughtful reflection; (b) reappraisal and reframing past and anticipated stressful events; and (c) problem solving, such as analyzing and solving personal problems. Each intervention begins with the same 5-minute introductory video and involves the completion of one 20-minute audio-guided lesson plus daily life homework practice (3-10 minutes) each day for 14 days. Lessons train specific techniques through didactic explanation and guided practices. After each lesson, participants will complete event-based assessments of stress and IBS distress. On Days 3 and 9 of the intervention program, study staff will contact participants by phone to answer training-specific questions, address difficulties, and encourage program adherence.

Post-Treatment Assessment. Participants in all three conditions will be asked to complete a week of EMA sampling in the week following the completion of the intervention programs, identical in form to their baseline EMA week. They will then come back into the lab for a post-intervention assessment of the same measures used during the baseline assessment, as well as to provide a second stool sample.

2-Month Follow-Up Assessment. Two months after the intervention, participants will complete a final week of EMA sampling. They will then be scheduled to complete a final assessment remotely, where they will complete the same trial outcomes assessment battery as they did at baseline and post-intervention. Additionally, participants will be asked to complete a treatment program evaluation survey measure at this time. After completing the study measures at the 2-month follow-up assessment, participants will be debriefed on the study aims and thanked for their participation.

CGI Assessment. A subset of participants (n=10-15) will be randomly selected to complete the Clinical Global Impressions Improvement Scale (CGI-I) at three time points - shortly after baseline, post-treatment, and at a 2-month follow-up. This assessment will be conducted by our Co-Investigator, Dr. David Levinthal. The CGI-I will incorporate baseline severity of IBS symptoms and the degree of clinical change relative to that baseline. Dr. Levinthal will provide these ratings of the patient's change in IBS symptoms (1=substantially improved to 7=substantially worse) at post-treatment and 2-month follow-up compared to baseline. These assessments will consist of open-ended questions related to the participant's IBS symptoms and the assessment will be based on a scale similar to Table 2 of the CGI article uploaded under Supporting Documents. The assessments will occur over Zoom or over the phone, and no recordings, neither audio nor visual, will be made. Dr. Levinthal will also be blind to the patient's treatment condition. Data collected from these clinical interviews will only be linked to the participant through study ID number, and Dr. Levinthal will complete the assessments over a secure web-based platform such as Qualtrics. The study team will provide Dr. Levinthal the contact information of the randomly chosen participant so that he can reach out to the participant to schedule these assessments. The team will then provide him the study ID number separately, ensuring that the contact information and study ID number are never linked together.

Cold Challenge Sub-Study. For participants who indicated that they would be willing to participate in the cold-challenge sub-study, they will be shown an instructional video outlining the cold-pressor task (as specified below). Once the participant submerges their left hand in the water, the experimenter will start a stopwatch and will ask the participant to rate their sensation intensity and distress verbally by showing them the visual chart. This will occur every 30 seconds up to 5 minutes, which at that point the participant will be asked to remove their hand. Once the participant's hand is on the towel, the experimenter will ask them to rate their sensation intensity and distress immediately and then again, every 30 seconds up to 2 minutes. They will then be allowed to move and dry their hand. To help the participant warm their hand up, the experimenter will recommend them to use a few strategies. These strategies include hand exercises (e.g., moving the hand in circles, clenching and releasing the hand), massaging the hand, and placing the hand under an armpit or a warm area of the body.