Upgrade Your Vagus Nerve

The interesting thing about this book isn't only what it says — it's who wrote it. Navaz Habib's follow-up to Activate Your Vagus Nerve is co-authored with J.P. Errico, an inventor closely tied to the development of non-invasive vagus nerve stimulation technology. That pairing is the book's identity: consumer self-help meeting someone who has actually engineered stimulation devices, which pulls the second book noticeably closer to the hardware than the first.

Where Activate taught you to assess and support vagal function through lifestyle, Upgrade leans into measurement and modern tools. Heart rate variability (HRV) is the spine of the book — the idea that you can quantify vagal tone and track whether an intervention moves it — and it folds in newer science and the growing menu of non-invasive electrical, acoustic, and breath-based methods. It is the more technically ambitious of the two.

That ambition is also where a careful reader stays alert. Errico's involvement lends real device expertise, but a commercial proximity to the technology is worth holding in mind when the tone turns enthusiastic. And like much in the functional-medicine genre, some protocols run ahead of the trial evidence — plausible, mechanism-based, and often reasonable, but not the same as proven. Treated as informed experimentation rather than settled medicine, it's genuinely useful.

On this shelf: the natural next step after Activate, and the most device-curious of the practical titles — a good bridge from lifestyle self-help toward the clinical references and the taVNS evidence itself.

Best for: readers who liked Activate and want the newer, HRV-and-stimulation-focused material — especially anyone weighing a non-invasive device.