S2Y Research Library
Peer-reviewed and registered studies behind S2Y content — 24 entries, continuously updated. Last updated: October 7, 2026.
Why this page exists
Most health pages cite a source or two and move on. We do the opposite: we maintain a structured, open index of the studies our content rests on, so that journalists, clinicians, researchers, and readers can inspect the evidence directly instead of trusting a repeated claim.
Every entry below lists the study type, the population studied, a key finding phrased in the hedged language the underlying design supports, and at least one stated limitation. Each row links to a primary record — a PubMed entry, a DOI, or a registered trial — that we opened and checked. Nothing here is included on the strength of a secondary summary alone.
What this page is not: it is not a clinical guideline, not a complete systematic search of the literature, and not medical advice. Inclusion means a study exists and reports what we describe — not that its finding is definitive. See our Editorial Policy for how we handle sourcing and corrections.
Prefer the raw data? Download the full CSV (topic, title, year, type, population, key finding, limitation, source).
Browse by topic
- Headache & Migraine (4)
- Sleep (2)
- Cognition & Stress (3)
- Autonomic / POTS (3)
- Long COVID & COVID (7)
- Safety & Reviews (3)
- Cardiac & Inflammation (2)
Headache & Migraine (4 studies)
Sleep (2 studies)
Cognition & Stress (3 studies)
Autonomic / POTS (3 studies)
Long COVID & COVID (7 studies)
Safety & Reviews (3 studies)
Cardiac & Inflammation (2 studies)
Headache & Migraine
Type: Randomized, double-blind, sham-controlled · Population: Episodic migraine (multicenter)
Key finding: Pain-free rates at 30 and 60 minutes favored active stimulation over sham; the pre-specified 120-minute primary endpoint was not significant.
Limitation: Studied a specific 5 kHz cervical device protocol; not generalizable to other stimulation parameters.
Type: Prospective open-label pilot · Population: Migraine patients with sleep disturbance
Key finding: Improvements in migraine frequency and sleep measures were reported in an uncontrolled setting.
Limitation: No sham control; placebo and regression-to-mean effects cannot be excluded.
Type: Systematic review and meta-analysis · Population: Pooled migraine trials
Key finding: A favorable signal for non-invasive VNS in migraine was reported, with a generally tolerable safety profile.
Limitation: Trial heterogeneity and small samples limit certainty; device protocols varied between studies.
Type: Randomized sham-controlled (subgroup analysis) · Population: Episodic cluster headache
Key finding: A signal of benefit was reported in the episodic subgroup; results were inconsistent in chronic cluster headache.
Limitation: Subgroup findings are exploratory and require replication.
Sleep
Type: Randomized controlled trial · Population: Primary insomnia
Key finding: Reported improvement in sleep-quality measures versus control.
Limitation: Single small study; device parameters differ from other protocols.
Type: Randomized clinical trial · Population: Chronic insomnia disorder
Key finding: A randomized trial reported improvement in insomnia outcomes versus control.
Limitation: Further large multicenter trials are needed; an auricular protocol may not transfer to cervical stimulation.
Cognition & Stress
Type: Randomized crossover study in healthy adults · Population: Sleep-deprived healthy volunteers
Key finding: Improvements in cognitive task performance under sleep-deprivation stress were observed.
Limitation: Healthy-adult model; effects under clinical conditions are not established.
Type: Experimental study in healthy adults · Population: Healthy volunteers (30 Hz protocol)
Key finding: Changes in auditory and visual task performance and some autonomic measures were observed.
Limitation: Healthy-adult outcomes do not establish therapeutic benefit in disease.
Type: Randomized preliminary study · Population: PTSD (small sample)
Key finding: Signals on inflammatory markers and symptoms after trauma-script exposure were observed.
Limitation: Very small preliminary sample; findings require replication in larger trials.
Autonomic / POTS
Type: Randomized, double-blind, sham-controlled · Population: Women with POTS (n≈26)
Key finding: Reduced orthostatic heart-rate rise versus sham (about 18 vs 32 bpm), with improved HRV and reduced inflammatory markers in this cohort.
Limitation: Small sample; 100% female cohort; tragus protocol; generalization requires larger trials.
Type: Comprehensive review · Population: Adult and adolescent POTS
Key finding: Reviews sympathovagal and anti-inflammatory mechanisms and summarizes ongoing registered trials.
Limitation: Mechanistic framing from reviews does not establish clinical efficacy.
Type: Registered clinical trial (ongoing) · Population: Adolescents 12–19 with POTS
Key finding: Ongoing study assessing symptom scores and tilt-table endpoints; results pending.
Limitation: Registration record; no efficacy conclusions can be drawn yet.
Long COVID & COVID
Type: Open-label preliminary study · Population: Long COVID patients meeting ME/CFS criteria (14 evaluable)
Key finding: 8 of 14 evaluable participants met treatment-success criteria, with reported quality-of-life and fatigue improvements.
Limitation: Open-label without sham control; small sample; placebo effects cannot be excluded.
Type: Single-arm preliminary study · Population: Women with long COVID (n=24)
Key finding: Immediate improvements in cognition, anxiety, depression, and sleep were reported; fatigue improved at one-month follow-up.
Limitation: Single-arm design; female-only cohort; no sham control.
Type: Single-arm preliminary study · Population: Long COVID patients
Key finding: All participants reported notable improvement; investigators hypothesized a sympathetic-reset mechanism.
Limitation: Uncontrolled preliminary design; the proposed mechanism remains hypothetical.
Type: Registered randomized controlled trial (ongoing) · Population: Long COVID patients
Key finding: Compares two transcutaneous stimulation parameter sets for fatigue, headache, and cognition; results pending.
Limitation: Registration record; no efficacy conclusions can be drawn yet.
Type: Registered clinical trial (ongoing) · Population: Long COVID patients
Key finding: Ongoing controlled evaluation of transcutaneous vagus nerve stimulation; results pending.
Limitation: Registration record; no efficacy conclusions can be drawn yet.
Type: Randomized sham-controlled trial (preprint) · Population: Early COVID-19 (n=320)
Key finding: The preprint reported favorable symptom and inflammatory-marker dynamics versus sham in early infection.
Limitation: Preprint: not yet peer-reviewed; findings require independent replication.
Type: Animal mechanistic study · Population: SARS-CoV-2-infected hamsters
Key finding: Reported lower lung TNF-α and improved oxygenation and 14-day survival signals.
Limitation: Animal model; effects in humans are not established.
Safety & Reviews
Type: Systematic review of safety · Population: Pooled taVNS/tcVNS studies
Key finding: A generally well-tolerated short-term safety profile was reported, with mostly mild local adverse events.
Limitation: Mostly short-term exposure; rare events may be under-detected; device heterogeneity.
Type: Consensus statement · Population: tVNS research community
Key finding: Defines required reporting of electrode, waveform, frequency, intensity, duration, and adverse events.
Limitation: Standard-setting document; not an efficacy study.
Type: Parameter-comparison study in humans · Population: Healthy participants (10–150 Hz; 4 vs 20 min)
Key finding: No universally optimal frequency was identified; 20-minute sessions did not show stronger overall autonomic effects than shorter sessions.
Limitation: Exploratory healthy-adult study; disease outcomes were not evaluated.
Cardiac & Inflammation
Type: Review · Population: Preclinical and clinical cardiovascular studies
Key finding: Summarizes anti-inflammatory mechanisms and cardiovascular endpoints of low-level tragus stimulation.
Limitation: Review of heterogeneous evidence; does not establish treatment efficacy.
Type: Animal mechanistic study · Population: Autoimmune myocarditis model
Key finding: Vagal signaling via α7-nAChR reduced inflammation and fibrosis in the model.
Limitation: Animal model; not transferable to human therapy.
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