Mechanisms of acupuncture analgesia for clinical and experimental pain.

There is convincing evidence that acupuncture (AP) is effective for the treatment of postoperative and chemotherapy-induced nausea/vomiting, as well as postoperative dental pain. Less convincing data support AP's efficacy for chronic pain conditions, including headache, fibromyalgia and low back pain. There is no evidence that AP is effective in treating addiction, insomnia, obesity, asthma or stroke deficits. AP seems to be efficacious for alleviating experimental pain by increasing pain thresholds in human subjects and it appears to activate analgesic brain mechanisms through the release of neurohumoral factors, some of which can be inhibited by the opioid antagonist naloxone. In contrast to placebo analgesia, AP-related pain relief takes some time to develop and to resolve. Furthermore, repetitive use of AP analgesia can result in tolerance that demonstrates cross-tolerance with morphine. However, it appears that not all forms of AP are equally effective for providing analgesia. In particular, electro-AP seems to best deliver stimuli that activate powerful opioid and nonopioid analgesic mechanisms. Thus, future carefully controlled clinical trials using adequate electro-AP may be able to provide the necessary evidence for relevant analgesia in chronic pain conditions, such as headache, fibromyalgia, irritable bowel syndrome and low back pain.