described in the medical writings The Yellow Emperor’s Classic of Internal Medicine1 around 200 BC. As early as 5000 years ago, stones were sculpted and formed into crude needles to be used as medical instruments.2 In time, other materials, including bamboo, fish bones, bronze, gold, and silver, have been refined into acupuncture needles. Acupuncture is based on the idea that living beings have an inner energy, known as Qi (pronounced chee), and it is the flow of this inner energy that sustains them. According to traditional Chinese medical philosophy, balanced Qi is vital to optimal health; illness and disease are caused by the imbalance or interruption in the flow of Qi. Although acupuncture was developed for prevention of illness, it is useful in managing disease symptoms by reintroducing balanced flow of Qi, its main focus. From the Division of General Internal Medicine, Mayo Clinic, Rochester, MN. Mayo Clin Proc. n October 2013;88(10):1141-1146 n http://dx.doi.org/10.1016/j.mayocp.2013.06.009 www.mayoclinicproceedings.org n ª 2013 Mayo Foundation for Medical Education and Research 1141 CONCISE REVIEW FOR CLINICIANS Jesuit missionaries introduced acupuncture to Europe in the 17th century, when they returned from China. The Jesuits were active in disseminating the idea and practice of acupuncture throughout Europe. In addition, traveling physicians helped pioneer acupuncture use in Europe.3 In the United States, acupuncture gained public and professional attention in 1971, when New York Times reporter James Reston wrote about his experience with acupuncture after an emergency appendectomy in China.4 The operation was a success, but Reston soon had a considerable amount of postoperative pain and bloating. To provide relief, Chinese physicians offered acupuncture as a therapeutic modality. Reston, impressed by the effectiveness of this “ancient” procedure, described the overall improvement of his symptoms with no recurrence afterward. Through his newspaper article, he exposed countless Americans to acupuncture for the first time. HOW MIGHT ACUPUNCTURE WORK? Anatomically, acupuncture points have been reported to correspond to cutaneous areas of high electrical conductivity and distinct histologic differences compared with adjacent tissue.5 There are many theories that may explain how acupuncture works. Gate Control Theory of Pain This theory postulates that specific nerve fibers transmit a pain signal to the brain via the spinal cord, and input of other nerve fibers can inhibit the pain signal transmission.6 Acupuncture is thought to stimulate inhibitory nerve fibers for a short period, thus reducing transmission of the pain signal to the brain. Endorphin Model During the 1970s, researchers isolated endogenous endorphins in the central nervous system. Clinical studies reported that inserting acupuncture needles into specific acupuncture points triggered the production of endorphins in cerebrospinal fluid after patients underwent acupuncture treatments.7-9 The pain-alleviating effects of acupuncture were reduced when naloxone was used to pretreat the patient, which may indicate that acupuncture-induced analgesia may be partly mediated through endogenous opioids.10 Recent research has found that traditional Chinese medicine acupuncture therapy has a direct effect in the up-regulation of m-opioid receptor binding availability in the central nervous system compared with placebo (sham) acupuncture.11 This finding may help explain some of the analgesic effects seen with acupuncture therapy. Neurotransmitter Model Research in animals has found that acupuncture can modulate serotonin, norepinephrine, and neurons that transmit or secrete g-aminobutyric acid.12-15 It is postulated that through the neurotransmitter model, acupuncture can be efficacious for treatment of depression, anxiety, and addiction. Other Theories Other theories postulate that acupuncture indirectly influences the autonomic system. Acupuncture treatment can affect respiration, heart rate, blood pressure, circulation, and immune function.16 Research indicates the increased electrical conductivity of tissues along acupuncture meridians.5 This result suggests that manipulation of the acupuncture meridians with needles may modulate the transmission of certain signals within the body. The current scientific theories provide a basis for stating that acupuncture has an effect on the nervous system, but its effects cannot be explained with a single mechanism. IS ACUPUNCTURE SAFE? Modern acupuncture needles are thin and flexible and are made of solid surgical stainless steel. Unlike hypodermic needles, acupuncture needles are finely tapered, allowing them to slide smoothly into the skin (Figure). Certain acupuncture needles are thinner than the average strand of human hair. Acupuncture in the developed parts of the world involves single-use, disposable needles packaged and sealed by the manufacturer in sterile conditions. Although case reports have highlighted major adverse events, such as organ puncture, infections, and bleeding complications, more recent, larger cohort studies using universal precautions have not found a significant complication rate. In a 2001 study of more than 34,000 acupuncture treatments in the United Kingdom, no serious adverse MAYO