Acupuncture is increasingly being practised as a complementary therapy, but its efficacy remains controversial and its physiological mechanisms of actions are largely unknown.

Several studies have been published to find evidence for the existence of acupuncture points and establish visual proof of the physical existence of meridians. In 1984 Dung observed that there were no particular structures under the acupoints, but he found out that nerve bundles were involved in almost all such locations. In 1996, using histological analysis, Croley showed that there was a high concentration of dermal papillae containing capillary loops with sympathetic nerve endings. In 2007, Helene Langevin’shistochemical examination demonstrated that subtle differences in acupuncture-needle manipulation techniques can affect cellular responses in mouse subcutaneous connective tissue.

Recent neuroimaging trials have shown altered functional brain responses to acupuncture in sensory, affective, cognitive and inhibitory regions, often including neural networks for pain perception and transmission. These studies have allowed researchers to better understand how acupuncture can treat specific diseases. In 2010, Napadow monitored the effects of acupuncture on human brain by functional MRI: his results suggested that acupuncture mobilizes a limbic-paralimbic-neocortical network and its anti-correlated sensorimotor-paralimbic network across multiple levels of the brain.

Furthermore, acupuncture has been shown to have several endocrine effects and affect neurotransmitter activity. Following Han's work, many authors have reported the release of endogenous opioid peptides in antinociceptive pathways (the arcuate nucleus, the periaqueductal gray, the nucleus raphe magnus and the descending inhibitory pathways) during acupuncture. In 2014, Wu localized ATP release at acupoints after acupuncture, demonstrating that acupuncture is related to neural regulation based on ATP. In 2008, Thomas demonstrated that acupuncture stimulation could reduce oxidative damage in pathological conditions. In 2011, Wang discovered that acupuncture has an anti-apoptotic effect by elevating the Bcl-2/Bax ratio.

More recent studies have proved that acupuncture has local and systemic effects mediated by nervous, neuroendocrine and immune systems, but its mechanisms are still far from being fully understood.