The Science Behind Acupuncture's Effectiveness for Migraine

Clinical studies show that acupuncture can reduce pain intensity, duration, emotional comorbidity, and days of acute medication intake. Neuroimaging studies suggest that acupuncture may alter abnormal functional activity and connectivity of various brain networks, and may reduce neuroinflammation, regulate peripheral and central sensitization, and normalize abnormal brain activity, thereby preventing pain signal transmission. (This means that it is harder to trigger a migraine after acupuncture.)

there is a lot more at the link

Improving vagal activity modifies parts of the brain that control unhealthy habits.

I’m referencing this article in my writing project and covered it in the blog. 

I measure HRV in the clinic and this study supports using HRV as a measure of frontal brain activity, a part of the brain that can regulate unhealthy behaviors. "Epidemiologically, high vagal activity, indexed by greater heart rate variability (HRV), independently predicts reduced risk of Global Burden of Disease (GBD) and better prognosis in GBD.”

So acupuncture and other measures to improve vagal activity and lowers stress helps to get rid of unhealthy habits. Perhaps this is why it is a mainstay in smoking cessation.