The Short-Term Effects of Transcutaneous Auricular Vagus Nerve Stimulation in Female Patients with Functional Constipation and Myofascial Pain Syndrome: A Randomized Clinical Trial

Introduction The management of chronic constipation when it coexists with chronic pain syndrome is challenging because of complex pathophysiologic and constipating analgesic side effects. Transcutaneous auricular vagus nerve stimulation (taVNS) is an effective neuromodulation method to modulate gastrointestinal function and pain processing by targeting vagal pathways. Accordingly, this study evaluated the short-term effects of taVNS in patients with functional constipation (FC) comorbid with myofascial pain syndrome (MPS). Materials and Methods A total of 38 female participants with FC and MPS (aged 20–50 years) were randomly allocated (1:1) using a computer-generated randomization to either taVNS or sham-taVNS groups. Participants received the intervention for 30 minutes, five days a week for two weeks. The complete spontaneous bowel movements per week (CSBMs/week) as the primary outcome was assessed at baseline and after the treatment. Secondary outcomes were Wexner constipation scores (WCS), patient assessment of constipation quality of life (PAC-QoL) score, visual analogue scale (VAS), pressure pain threshold (PPT), and heart rate variability (HRV). Results The result of analysis of covariance (ANCOVA) showed that taVNS significantly and clinically improved CSBMs/week compared with the sham-taVNS ( p = 0.007; Cohen d = 0.97, 95% CI 0.26 – 1.66). The mean increase of CSBMs/week was 1.65 times compared with the baseline and 1.37 times compared with the sham-taVNS (MCID = 1.3 times). Moreover, the taVNS group had greater reduction in WCS and VAS compared with the sham group. In the HRV analysis, the taVNS enhanced high frequency (HF) and decreased low frequency (LF) and the LF/HF ratio compared with the sham-taVNS. However, there was no substantial difference in the PPT and PAC-QoL between groups. Conclusions These promising findings provide preliminary evidence that taVNS may be an effective nonpharmacologic intervention in female patients with FC coexisting with chronic pain conditions, particularly MPS. Further large-scale studies with longer follow-up and mechanistic assessments are warranted. © 2026 International Neuromodulation Society.