Effects of left and bilateral transcutaneous auricular vagus nerve stimulation on pain, mood, and autonomic nervous system in female patients with fibromyalgia: a randomized controlled trial

Introduction Fibromyalgia Syndrome (FMS) is a complex disease characterized by widespread pain, fatigue, emotional disturbances, and autonomic dysfunction. Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) has emerged as a potential noninvasive approach to modulate FMS-related symptoms.Purpose To compare the effects of left and bilateral taVNS on pain, mood, functionality, and autonomic nervous system (ANS) activity in individuals with FMS.Methods Forty female individuals with FMS were assigned to either a left (n = 20) or a bilateral (n = 20) taVNS group. Both received 11 sessions of taVNS targeting the tragus and concha regions (30 minutes each, 25 Hz, 300 µs) over nonconsecutive days, excluding weekends and menstrual periods. Visual Analog Scale (VAS), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), and Fibromyalgia Impact Questionnaire (FIQ) were assessed. ANS activity was evaluated via heart rate variability (HRV). After 11 sessions of taVNS, a 2-week follow-up was performed.Results No significant differences were observed between groups except for FIQ and BAI on day 28 (p = .002–0.008). Both groups showed significant within-group improvements in VAS (r = 0.87–0.94; p < .001), BDI (r = 0.46–0.71; p < .001), FIQ (r = 0.95–0.99; p < .001), and BAI (r = 0.69–0.94; p < .001) scores. Parasympathetic Nervous System (PNS) (p = .365–0.776) and Sympathetic Nervous System (SNS) (p = .598–0.880) indices, which are the subparameters of HRV, showed no significant between-group differences, with small effect sizes (r < 0.15).Conclusion Both stimulation protocols effectively reduced pain and improved mood and functionality in fibromyalgia, indicating a safe, noninvasive adjunctive treatment option.ClinicalTrials.gov (Identifier: NCT06871306)