In 2013 a study was done that determined that acupuncture can cause your brain to release neuropeptides- molecules that allow neurons and effector cells the communicate.
“Dr. Auth. "Your nervous system is divided between the sympathetic and parasympathetic nervous system. Our sympathetic nervous system is known for 'fight or flight;' when the sympathetic nervous system is on, our blood pressure goes up, as does the body’s stress hormone, cortisol," she says. "Acupuncture can encourage the body to let the parasympathetic nervous system take over — allowing the heart rate to slow down, and blood pressure and cortisol levels to drop."
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