Optimization of taVNS Intervention Strategies for Refractory Constipation

Inclusion Criteria (Revised) Diagnosis of Functional Constipation (FC): Meets Rome IV criteria for functional constipation.

Low CSBM frequency during screening: During the 2-week screening/run-in period, has ≤2 complete spontaneous bowel movements (CSBMs) per week, based on daily diary.

Inadequate response to prior therapy: History of ≥3 months of prior constipation treatment (e.g., laxatives and/or prokinetic agents) with inadequate response (persistent constipation symptoms and/or persistently low CSBM frequency) as documented by medical history and/or records.

Age: 18 to 80 years. Ability to comply: Able and willing to comply with study procedures (including stimulation sessions and diary completion).

No concurrent clinical trial participation: Not participating in another interventional clinical trial during the study period.

Informed consent: Provides written informed consent. Exclusion Criteria (Revised) Organic/secondary causes of constipation: Evidence or history of gastrointestinal organic disease (e.g., inflammatory bowel disease, colorectal tumor, congenital megacolon) or other conditions likely to cause secondary constipation, including endocrine/metabolic disorders (e.g., uncontrolled hypothyroidism, uncontrolled diabetes) or neurological disorders (e.g., Parkinson's disease, spinal cord disorders).

Medications causing constipation (unless stable): Current use of medications known to cause constipation (e.g., opioids, anticholinergics) that cannot be discontinued or kept stable during the study, in the investigator's judgment.

Opioid use disorder or chronic opioid use: History of substance abuse or chronic opioid use that may affect bowel function.

Severe psychiatric conditions or safety risk: Current severe psychiatric disorder requiring urgent intervention, or risk of self-harm/suicide as assessed by a qualified clinician.

Contraindications to taVNS or ear stimulation: Significant ear disease or skin lesions/infection at the stimulation site, or other contraindications to the study device/procedure.

Implanted electronic medical devices: Presence of implanted electrical devices (e.g., pacemaker, implantable cardioverter-defibrillator) or other conditions where electrical stimulation is contraindicated.

Pregnancy or lactation: Pregnant or breastfeeding women. Serious comorbidities that may interfere: Severe or unstable medical conditions that could interfere with participation or outcome assessment (e.g., significant cardiovascular disease/arrhythmia, coagulation disorders or regular anticoagulant therapy, severe hepatic/renal impairment, organ failure).

Cognitive/communication impairment: Cognitive impairment, aphasia, or other conditions preventing valid consent or reliable diary completion.

Investigator discretion: Any condition that, in the investigator's opinion, makes the participant unsuitable for the study.