What the Vagus Nerve Industry Gets Wrong

Introduction

This article is a follow-up to what I previously wrote about the vagus nerve and a transcutaneous vagal nerve stimulator I am using. This is a harder look at what the science can validate. It isn’t meant to refute what I wrote. It gives a more complete picture.

Market analyses put the vagus nerve stimulation industry somewhere between roughly $1.4 billion and $2.8 billion by the early 2030s, depending on which forecast you trust. More than 125,000 people have received implanted devices, primarily for epilepsy rather than depression. Implanted VNS has FDA approval for epilepsy and depression, and non-invasive VNS has FDA clearance for certain headache indications. Major medical centers promote these devices as advanced treatments for conditions that don't respond to medication (Coherent Market Insights 2026; Verified Market Reports 2026; Afra 2021; Mayo Clinic 2024; FDA 2015).

I have a close relative who is several years past a stroke with persistent neurological deficits. They had an implanted vagal nerve stimulator and thought it helped. The study is over now, and they have to spend several thousand dollars if they want to keep using the stimulator already in their body. That is troubling, especially when that cost wasn't fully disclosed on the front end.

When I dug into the approval process for depression, I found something unsavory. The approval trial had no control group. The FDA's scientific review team repeatedly rejected the application. The device division director overruled them and approved it anyway. A Senate Finance Committee investigation later called the process "troubling" (Grassley and Baucus 2006; Shuchman 2007).

Years later, when researchers ran a large sham-controlled trial (meaning the device was compared against a fake version designed to mimic it), active VNS did not significantly beat sham on the primary outcome. Medicare had already looked at the earlier evidence and declined routine coverage for treatment-resistant depression (Conway 2024; CMS 2007).

Meanwhile, studies on breathing exercises, cold exposure, and even humming were showing comparable effects on the same nervous system pathways. Those studies were coming out of universities in Europe and Asia, funded by research grants, published in smaller journals. No one was making billions teaching people to breathe at six breaths per minute.

At 75, I've learned that when financial incentives and scientific evidence point in opposite directions, it pays to look closer. I spent the last few months doing exactly that.

What the Wandering Nerve Actually Does

Your vagus nerve earned its name from the Latin word for wandering. It originates deep in your brainstem and threads down through your neck into your chest and abdomen, touching nearly every major organ along the way.

The nerve works as a two-way communication system. Roughly 80% of the fibers carry information up from your organs to your brain. Your heart, lungs, and digestive tract are constantly sending status reports. The remaining 20% of fibers carry commands back down, controlling heart rate, digestive function, inflammatory responses, and how quickly you recover from stress.

When this system works well, you feel it. Stress hits, you respond, then you recover. Your heart rate speeds up when needed and slows back down when the threat passes. Your digestion processes food efficiently. Inflammation stays balanced. Sleep comes easily.

When vagal function declines, everything shifts. The stress response gets stuck in the on position. Your heart rate becomes rigid instead of flexible. Inflammation rises. Digestion slows. Sleep fragments. You feel wired but exhausted at the same time.

Researchers started measuring heart rate variability as a window into vagal tone decades ago. The logic seemed sound: if your vagus nerve controls how quickly your heart rate shifts beat to beat, then higher variability should reflect stronger vagal influence. That assumption became so widespread that HRV and vagal tone became almost interchangeable terms in both research and clinical practice.

A 2021 study from Case Western Reserve University challenged that assumption directly. The researchers measured vagal nerve activity in rats using direct nerve recordings, not HRV. They found no consistent correlation between tonic vagal activity and common HRV metrics. A 2025 study found that short-duration transcutaneous auricular stimulation reduced HRV while presumably activating the vagus nerve (Marmerstein 2021; Badran 2025).

These findings don't mean HRV is useless. They mean we've been less certain about what we're measuring than we thought. The device industry built an entire market on the premise that stimulating the vagus nerve would increase HRV and therefore improve autonomic function. That premise may be backwards.

When Devices Work and When They Don't

The clearest evidence for implanted vagus nerve stimulators comes from epilepsy. Two main trials, E03 and E05, tested the devices in patients with drug-resistant seizures who hadn't responded to medication (Ben-Menachem 1994; Handforth 1998).

In the E03 trial, 114 patients received either high-intensity stimulation or low-intensity stimulation that served as a control. After three months, the high-stimulation group showed a 24.5% reduction in seizure frequency compared to 6.1% in controls. That's an 18.4% treatment effect. Modest but real (Ben-Menachem 1994).

The E05 trial replicated the finding with 196 patients. High stimulation produced a 27.9% reduction compared to 15.2% with low stimulation, for a 12.7% treatment effect. About one in three patients in the active groups achieved a 50% or greater reduction in seizures (Handforth 1998).

The long-term observational data looks better. In one large retrospective series, patients had a mean 55.8% reduction in seizure frequency after an average of nearly five years. Whether that reflects the device working better over time or patients who didn't benefit dropping out remains hard to separate. But for someone with severe epilepsy who hasn't responded to drugs, these numbers matter (Elliott 2011).

The mechanism remains uncertain. Even the Iowa State Medicaid guidelines note this explicitly in their coverage decisions. But the clinical benefit is reproducible across trials and research groups. I can't dismiss that.

The depression evidence tells a different story.

The approval trial for FDA approval, called D02, enrolled 235 patients with treatment-resistant depression. All patients received the active device for 10 weeks. No control group. No sham. The study measured changes from baseline using standard depression rating scales (Rush 2000).

Response rates were 30% to 40% depending on which scale you used. That sounds promising until you remember that depression has a substantial placebo response rate, often 30% to 35% in antidepressant trials. Without a control group, you can't separate device effects from natural fluctuation, regression to the mean, or placebo.

The FDA's scientific review team repeatedly rejected the application. They asked for a controlled trial. The device division overruled them and approved it based on "treatment need" for patients who had exhausted other options. That's the polite term for approving something without adequate evidence.

The agency asked for a post-approval study. Nearly 20 years after approval, a large sham-controlled trial finally appeared. The RECOVER trial, published in 2024, enrolled 493 patients and randomly assigned them to active stimulation or sham for a year. The primary outcome was percent time in MADRS response between months 3 and 12, not simple remission (Conway 2024).

Active VNS did not significantly beat sham on that primary outcome. The active group spent 18.9% of the measured period in MADRS response compared with 16.3% in the sham group. Some secondary outcomes favored active VNS, but the main endpoint failed (Conway 2024).

Medicare examined the evidence and declined to cover the devices for depression. A Senate Finance Committee investigation in 2006 found that eight of the nine authors who wrote a major review supporting VNS for depression were paid consultants for the device manufacturer. They didn't disclose those relationships in the publication. The lead author was the journal's editor-in-chief. He later joined the company's advisory board (CMS 2007; Grassley and Baucus 2006).

When institutions were asked to comment, the responses were revealing. McGill University's guidelines call the depression evidence "insufficient." Major academic medical centers now offer VNS only as part of comprehensive treatment programs for the most resistant cases, alongside multiple other interventions. These are institutions known for adopting new technologies early when the evidence supports it.

The pattern repeats with other conditions. The devices have moved into markets for stroke rehabilitation, rheumatoid arthritis, and heart failure based on open-label studies and surrogate markers, not controlled trials showing clinical benefit.

I'm not saying the devices are worthless. In my earlier article I noted that I am using a transcutaneous device myself. For severe epilepsy, VNS is a legitimate option. For cluster headaches, the non-invasive version called gammaCore has randomized trial evidence, especially in episodic cluster headache. The effects are not overwhelming, but when you're dealing with excruciating pain that cycles through your day, partial relief can matter (Ben-Menachem 1994; Handforth 1998; Elliott 2011; Silberstein 2016; Goadsby 2018; FDA 2015).

But the industry has positioned these devices as broadly effective nervous system regulators for nearly any condition involving stress, inflammation, or autonomic dysfunction. That claim doesn't match what the controlled trials actually show.

What Works Without Wires

Here's where the story gets interesting. The same nervous system pathways these devices target respond to inputs you can control yourself. The research on these approaches has been growing steadily for two decades, published across hundreds of trials, yet most physicians never hear about it.

A 2022 meta-analysis examined 223 studies on voluntary slow breathing and its effects on autonomic function. The analysis included nearly 10,000 participants across randomized controlled trials. Slow breathing consistently increased parasympathetic activity, reduced stress markers, and improved measures of cardiovascular function (Laborde 2022).

The research points toward roughly six breaths per minute. You breathe in for about five seconds, then breathe out for about five seconds. The exhalation should be slightly longer than the inhalation if possible. This pace maximizes respiratory sinus arrhythmia, the pattern where your heart rate speeds up slightly on the inhale and slows on the exhale. I have been training myself with the 4-7-8 technique, inhaling for 4, holding for 7, and slowly exhaling for 8 (Laborde 2022).

A 2024 study compared different breathing rates in athletes. Six breaths per minute produced the strongest autonomic effects, increasing high-frequency HRV components and reducing sympathetic activation markers. Five breaths per minute worked almost as well. Faster rates showed progressively less benefit (You 2024).

The mechanism involves multiple pathways. Slow exhalation activates baroreceptors in your carotid arteries that sense blood pressure. These receptors send signals up the vagus nerve to your brainstem, triggering a reflex that slows heart rate and promotes relaxation. Deep breathing also stimulates stretch receptors in your lungs that feed back through vagal pathways (Laborde 2022).

The time course matters. A 2021 study from the University of Geneva tested a single session of slow breathing in younger and older adults. After just five minutes, vagal tone increased and anxiety measures dropped in both age groups. The effects appeared within minutes and lasted for at least 30 minutes after the breathing stopped (Magnon 2021).

If you do this consistently, the effects build. A 2019 study had business students practice slow breathing before making decisions under stress. Those who used the technique showed better decision quality and maintained higher HRV during high-pressure situations compared to controls. The practice appeared to preserve cognitive function when the stress response would normally impair it (De Couck 2019).

Cold exposure works through different mechanisms and the evidence is more mixed. A 2023 systematic review and meta-analysis of the diving response found that cold-face and diving-type stimuli can increase cardiac vagal activity. A 2022 cold-face study also found bradycardia, higher HRV measures, and lower cortisol response after acute stress in healthy young adults (Ackermann 2023; Richer 2022).

The response is called the diving reflex. When cold water hits your face, specialized receptors trigger a parasympathetic surge that slows your heart rate and redirects blood flow to protect core organs. This reflex is strongest with cold face exposure and diving-type stimuli, and it can also show up during cold water immersion (Ackermann 2023; Richer 2022).

The timing is faster than breathing practices. Heart rate can drop within seconds of cold-face exposure. The effect is most pronounced early, then longer exposure can bring in more sympathetic stress physiology. For me, that argues for brief exposure rather than turning cold into another endurance contest (Richer 2022).

Combining the two practices is plausible, but I would treat that as an experiment, not a proven protocol. Slow breathing during cold exposure may help you stay calm under a physical stressor. Whether that transfers to other stress situations needs better testing.

Other practices show promise but with less research backing. Humming and chanting activate vagal pathways through a different route. The vibration from sustained vocal tones stimulates mechanoreceptors in your throat and chest that connect to the vagus nerve. A 2011 functional MRI study found that "Om" chanting deactivated the limbic system, the brain's emotional control center, in ways that resembled meditation (Kalyani 2011).

The effects appear quickly. A 2023 study found that 10 minutes of humming or "Om" chanting increased HRV and reduced cortisol levels immediately afterward. Whether these acute changes translate to long-term benefits with consistent practice remains untested in controlled trials (Trivedi 2023).

Transcutaneous auricular vagal nerve stimulation targets a branch of the vagus nerve that innervates part of the outer ear, specifically an area called the cymba conchae. Small electrical pulses delivered to this region can activate vagal pathways without surgery. This ear-based approach is not the same as gammaCore, the neck-based non-invasive device cleared for certain headache indications (Machetanz 2021; FDA 2015).

Parameters matter substantially. One parameter study found effects with bursts using 100 microsecond pulse widths and current around 2 milliamps at specific auricular locations. Higher intensity is not automatically better. Location, pulse width, current, and baseline autonomic state all appear to matter (Machetanz 2021; Badran 2025).

The time course for auricular stimulation differs from breathing or cold exposure. Effects build gradually over several minutes rather than appearing immediately. Some research shows that effects can persist after stimulation stops, suggesting a cumulative effect on nervous system regulation (Machetanz 2021).

The Institutional Bias Problem

The pattern I've described did not happen by accident. Device evidence is strongest in narrow indications, behavioral evidence is often ignored, and the financial incentives favor things that can be sold. That reflects structural bias in how medical research gets funded, published, and translated into practice.

Device and pharmaceutical companies fund a large share of intervention research. These companies have shareholders to answer to. They fund studies designed to get products approved and marketed, not to compare their products against free alternatives that can't be patented.

The result is a massive evidence gap. We have dozens of trials testing implanted VNS devices against sham surgery or standard care. We have hundreds of trials testing breathing techniques against inactive controls. What we don't have are head-to-head studies comparing the devices to the behavioral practices.

That absence is intentional. No company will fund research that might show an expensive implanted device works no better than breathing exercises you can learn in 10 minutes. The economic logic is obvious. The scientific and ethical logic should be equally obvious, but it gets ignored.

Academic medicine has become increasingly dependent on industry partnerships. Major medical centers compete for device company funding, consulting relationships, and speaking fees. When McGill or Cleveland Clinic remove VNS from their treatment algorithms, it represents a significant institutional decision to go against financial incentives. That it happens so rarely tells you how strong those incentives are.

The journal publication process reflects similar biases. The depression review I mentioned earlier, the one where eight of nine authors were paid consultants who didn't disclose it, was published in a major psychiatry journal. The editor-in-chief was the lead author. After the Senate investigation exposed the conflicts, the journal never retracted the paper. It remains in the literature, cited by other researchers as evidence supporting VNS for depression.

The FDA approval process has its own problems. The device division operates differently from the drug division. Device approvals often rely on smaller trials, shorter follow-up, and less rigorous evidence standards than drug approvals require. When a device gets approved despite the scientific review team saying no repeatedly, as happened with VNS for depression, it signals that factors beyond scientific evidence are driving decisions (Grassley and Baucus 2006; Shuchman 2007).

Medicare's refusal to cover VNS for depression shows what happens when someone actually applies consistent evidence standards. The agency looked at the same data the FDA approved and concluded the evidence didn't support routine use. That should have prompted a reevaluation of the approval. Instead, it created a situation where the device is legally approved but not covered by the largest payer in the healthcare system.

The messaging matters. When major medical conferences feature device presentations but barely mention breathing research, physicians form skewed impressions of what works. When patient advocacy groups receive device company funding, their educational materials emphasize device options. When journal advertising revenue depends on device companies, editorial decisions shift subtly toward covering topics those companies want covered.

The incentives explain plenty. The system rewards developing, promoting, and implanting devices. It doesn't reward teaching breathing techniques or cold exposure protocols. The evidence base we've accumulated reflects those rewards.

What I'm Actually Doing

I practice slow breathing most mornings for about 10 minutes. I sit comfortably, set a timer, and breathe at roughly six cycles per minute. I don't count obsessively. I focus on making the exhale slightly longer than the inhale and keeping the rhythm smooth. Some days my mind wanders. Some days I feel immediate calm. I keep doing it because the research shows effects build with consistency. I incorporate that practice with prayer. Meditation. I know they both have benefit for me personally and there is evidence that they are effective.

I do cold showers on occasion but not as much as I should. I am considering doing cold plunges but as of yet I do not own a cold plunge. I may do some in the lake near my house over the winter. I am generally chicken when it comes to that known shock.

I tried humming practice for several weeks. I found it awkward and wasn't convinced I was doing it effectively enough to matter. I may revisit it, but for now it's off my routine. Not everything that works in studies works for every person.

I use the transcutaneous vagal stimulator branded as Pulsetto which I wrote about in the earlier article. My current regimen is for at least 3 sessions of 25 minutes each every day. Some days more than 3 sessions. I like it. I’ve been doing that for more than a month. Check back in a year and see where I’m at. I view it as supplementary rather than foundational. Breathing is foundational.

I track HRV trends weekly using a Garmin device. I don't obsess over daily readings because the variability is high and influenced by sleep quality, exercise, stress, and factors I can't control. The weekly moving average gives me a sense of direction. I use the Polar H10 chest strap for more accurate heart-rate tracking during cardio and as a way to measure HRV in real time. I know the science, and I understand what I wrote above, but for me it may be a useful surrogate marker for vagal tone. If I see improvement, I note what I've been consistent with.

I pay more attention to how I actually feel. Energy levels, stress resilience, mental clarity, sleep quality. Those subjective measures matter more to me than any number on a screen. The data exists to inform my understanding, not to create new sources of anxiety.

Where This Leaves You

Your vagus nerve evolved to respond to natural inputs. Breath rhythm. Temperature changes. Physical vibration. Social connection. These inputs can activate regulatory pathways involved in stress recovery, heart-rate flexibility, and inflammatory control (Laborde 2022; Ackermann 2023; Richer 2022; Machetanz 2021).

The medical device industry has built a narrative that these natural inputs are insufficient for meaningful nervous system regulation. That real intervention requires technology, surgical implantation, electrical stimulation, ongoing medical management.

When you examine the actual evidence, that narrative breaks down. The controlled trials show modest effects for devices in specific conditions like epilepsy and cluster headaches. For depression, the largest randomized trial did not meet its primary endpoint. For general autonomic function, the comparison studies simply don't exist (Ben-Menachem 1994; Handforth 1998; Conway 2024; Silberstein 2016; Goadsby 2018).

Meanwhile, the research on breathing practices spans 223 studies and nearly 10,000 participants. The cold-exposure literature is smaller, but the cold-face and diving-response research shows measurable short-term changes in cardiac-vagal markers. These practices work through documented physiological mechanisms. They produce measurable changes in some of the same nervous system pathways the devices claim to target. And they cost nothing beyond the time to learn and practice them (Laborde 2022; Ackermann 2023; Richer 2022).

The research shows your autonomic function responds to consistent, accessible inputs. The challenge is cutting through the marketing noise to find what actually works. When I look at the evidence without the financial bias layered on top, the accessible practices deserve to be tried before the expensive alternatives.

Additional resources and supplementary research materials are available to Sage Matters subscribers. For personal guidance, wait for the Sage Matters clinical program to open, then work with the licensed clinical team before adding device-based stimulation or cold exposure if you have heart disease, arrhythmia, seizure history, an implanted device, uncontrolled blood pressure, or another medical risk.