A pre-specified interim analysis was conducted as planned, we calculated a P-value greater than 0.57 when comparing response rates between taVNS and sham group, resulting in an early termination of the study.

The worldwide prevalence of chronic constipation (CC) is 15%, and women are more likely to develop the disease than men. CC have a significant impact on quality of life and increase the burden of national health insurance. The conventional medication treatments are primarily symptom-specific and have limited efficacy. Previous small sample study had shown the therapeutic potential of transcutaneous auricular vagus nerve stimulation (taVNS) for irritable bowel syndrome with constipation (IBS-C). The aim of this study was to investigate whether taVNS could improve defecation condition and constipation symptoms in patients with CC.

Inclusion Criteria:

1. FC or IBS-C patients aged 18-75 years who meet the diagnostic criteria for Rome IV;
2. Complete spontaneous bowel movements (CSBMs) per week < 3;
3. No constipation medication used for at least 2 weeks prior to enrollment, not participated in clinical trials in the past three months, and no abnormal colonoscopy within the past 12 months in those with alarm symptoms.

Exclusion Criteria:

1. Have cognitive impairment, psychiatric disorders, or conditions that may affect patient cooperation;
2. Have a cardiac pacemaker implantation or other electronically implanted devices;
3. Prior taVNS treatment;
4. History of colorectal surgery, except for simple appendectomy;
5. Severe cardiovascular, hepatic, or renal disease;
6. Known malignancy;
7. Secondary constipation caused by medications and other diseases;
8. Pregnant or lactating women;
9. Refusal to sign an informed consent.

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