Transcutaneous Auricular Vagus Nerve Stimulation Shows Promise for Chronic Pain, but Evidence Remains Uneven Across Conditions

Chronic pain (搜索)搜索该疾病 affects approximately 30% of the global population and is increasingly recognized as an independent clinical entity rather than merely a symptom, characterized by complex nociceptive, neuropathic, and nociplastic mechanisms and frequent comorbidity with anxiety and depression. Against a backdrop of well-documented limitations of pharmacological treatments—including gastrointestinal injury, cardiovascular risks, addiction potential, and cognitive impairment—non-invasive neuromodulation has emerged as a prominent therapeutic strategy. Among these approaches, transcutaneous auricular vagus nerve stimulation (搜索)搜索该药品 (taVNS) has attracted growing attention since its introduction in 2000 as a non-pharmacological option for chronic pain.

A comprehensive narrative review published in the Journal of Pain Research synthesizes evidence across five major chronic pain (搜索)搜索该疾病 categories to systematically examine the mechanisms of action and clinical utility of taVNS. The review, conducted following the Scale for the Assessment of Narrative Review Articles (SANRA) guidelines, screened 1,916 records across PubMed/MEDLINE, Embase, Web of Science, and the Cochrane Library, ultimately yielding 44 eligible primary studies on taVNS and chronic pain.

Mechanisms of Action: A Multi-Target, Integrative Approach

The auricular branch of the vagus nerve (Arnold's nerve) is the only cutaneous branch of the vagus nerve, with nerve endings highly concentrated in the auricular concha region, particularly the cymba conchae. This accessible anatomical localization renders the auricular concha a practical target for taVNS. Approximately 80% of vagus nerve fibers are afferent, serving as a core bidirectional pathway connecting the central nervous system with visceral organs.

taVNS modulates nociceptive processing through four principal pathways. At the neurochemical level, it enhances GABAergic inhibitory transmission, activates the locus coeruleus–norepinephrine system, facilitates descending serotonergic modulation, and promotes release of endogenous opioid peptides including β-endorphin, enkephalin, and dynorphin. At the immunological level, taVNS engages the cholinergic anti-inflammatory pathway (CAP), in which vagal efferent signaling leads to acetylcholine release that binds to α7 nicotinic acetylcholine receptors on macrophages, inhibiting nuclear factor-κB signaling and downregulating pro-inflammatory cytokines including TNF-α (搜索)搜索该靶点, IL-1β, and IL-6查看药品详情.

At the neuroplastic level, taVNS upregulates brain-derived neurotrophic factor查看药品详情 (BDNF)-mediated synaptic plasticity and remodels thalamocortical connectivity. Functional MRI evidence demonstrates that taVNS strengthens functional coupling between motor-associated thalamic subregions and the rostral anterior cingulate cortex/medial prefrontal cortex, while weakening connectivity between occipital-linked thalamic subregions and the postcentral gyrus. At the network level, taVNS regulates the dynamic balance between the default mode network and salience network.

Clinical Evidence Across Pain Phenotypes

The review identifies a stratified pattern of efficacy. For musculoskeletal disorders, a 12-week sham-controlled randomized trial by Elsehrawy et al enrolling 68 bilateral knee osteoarthritis patients demonstrated sustained improvements in pressure pain threshold, nociceptive pain, neuropathic pain (搜索)搜索该疾病 markers, central sensitization inventory, physical function, and mood that persisted four weeks after treatment cessation. In chronic low back pain, a 3-month open-label pilot by Tavares-Figueiredo et al reported progressive, statistically significant pain reduction, with VAS falling by 16.1 mm at month 1 and 22.5 mm at month 3 (both P<0.001), and 51.9% of participants reaching the ≥20 mm VAS threshold for clinically meaningful pain relief.

For visceral pain, two randomized controlled trials in constipation-predominant irritable bowel syndrome (搜索)搜索该疾病 (IBS-C) demonstrated that taVNS relieved abdominal discomfort and defecatory dysfunction while restoring rectal sensation and normalizing the rectoanal inhibitory reflex. A multicenter, triple-arm randomized controlled trial by Shi et al enrolling 300 functional dyspepsia (搜索)搜索该疾病 patients found both 10 Hz and 25 Hz taVNS produced significantly higher clinical response rates than sham, with sustained benefits at week 12 follow-up.

However, the evidence is notably weaker for certain conditions. In fibromyalgia (搜索)搜索该疾病, the single available randomized controlled trial reported neutral between-group results, with the between-group difference in pain intensity narrowly missing statistical significance (P = 0.084). In rheumatoid arthritis (搜索)搜索该疾病, a large-scale, multicenter, double-blind, sham-controlled RCT by Baker et al failed to meet its primary endpoint (DAS28-CRP) in biologic-naïve patients with inadequate responses to conventional synthetic disease-modifying antirheumatic drugs.

A Proposed Stratification Hypothesis

Based on this heterogeneous evidence, the review proposes that pain conditions driven primarily by neuroinflammation and autonomic dysregulation—such as IBS, functional dyspepsia (搜索)搜索该疾病, and selected early-stage autoimmune disorders—are most responsive to taVNS. Conversely, disorders characterized by advanced tissue destruction or intractable central sensitization, such as advanced rheumatoid arthritis (搜索)搜索该疾病 and fibromyalgia (搜索)搜索该疾病, afford only partial symptomatic relief.

"taVNS preferentially targets neuroimmune inflammation and autonomic dysfunction, yet demonstrates limited efficacy against established structural damage or refractory central sensitization," the authors note. "This mechanistic heterogeneity explains variable clinical responses across pain subtypes."

Comparative Evidence in Neuropathic Pain

A separate systematic review and network meta-analysis, also published in the Journal of Pain Research, compared invasive and non-invasive neuromodulation techniques for chronic neuropathic pain (搜索)搜索该疾病. The analysis included 68 randomized controlled trials encompassing nine interventions: rTMS, tDCS, TENS, spinal cord stimulation (SCS), peripheral nerve stimulation (PNS), dorsal root ganglion stimulation (DRG-S), sham stimulation, no treatment, and conventional medical management.

In the primary analysis, PNS showed significantly greater pain relief than sham stimulation (SMD = −1.51, 95% CI: −2.57 to −0.46), no treatment, and conventional medical management. SCS was significantly superior to no treatment (SMD = −1.78, 95% CI: −2.83 to −0.72) and conventional medical management. rTMS, TENS, and tDCS also significantly reduced pain compared with sham stimulation. Based on SUCRA values, PNS ranked highest (80.7), followed by SCS (78.9) and rTMS (75.2).

Critically, the authors caution that confidence in all network estimates was rated very low using the CINeMA framework, primarily due to major concerns regarding heterogeneity. "Most comparisons among active interventions were not statistically significant, and these findings do not establish treatment superiority," the authors emphasize. Safety profiles differed by intervention type, with non-invasive approaches associated with headache (OR = 1.69, 95% CI: 1.31 to 2.19) and implantable techniques associated with infection risk (OR = 2.69, 95% CI: 1.17 to 6.21).

Future Directions

The taVNS review calls for standardized head-to-head trials to resolve cross-study inconsistencies in optimal stimulation frequency, noting that optimal frequency regimens appear phenotype-specific. The authors also advocate for multimodal neuroimaging and peripheral cytokine profiling to delineate distinct mechanisms across inflammatory and nociplastic pain, and for biomarker-guided stratification to identify responsive patient subgroups. Both reviews underscore the need for larger, rigorously designed randomized controlled trials with longer follow-up durations before taVNS or any neuromodulation technique can be confidently positioned within routine clinical practice.