Like a highway system, the vagus nerve branches profusely from your brain through your organs to marshal bodily functions, including aspects of mind such as mood, pleasure, and fear.
However, some people have taken the vagus nerve’s expansive bodily influence as an invitation to engage in pseudoscience. In some corners of the internet, so-called polyvagal therapy—physical or breathing exercises that some claim reset the vagus nerve—is proposed to address just about any disorder of the mind or body. There’s little to no evidence that these popular remedies are anything but placebos.
Because of the placebo effect, all you really need for anything that’s not outright poison to have a positive effect on average is a convincing enough practitioner. Ideally people have narrow criteria for judging that, but it’s just so ripe for exploitation, every scammer can try a different tack, and some are bound to slip through.
IMO, the solution is a system of tight regulations on the definition of medical advice and the qualifications required to dispense it. I can also see that this one specifically would be hard to legislatively prevent without training and licensing yoga teachers, for example.
I'm trying to find studied that show it isn't statistically different from a placebo, but doesn't seem to be well studied. Can anyone share some well designed studies?