From a modern scientific reductionist point of view we do not have a global or comprehensive explanation of how acupuncture works. Some of the partial explanations are:
Gate theory of pain: this theory postulates that Acupuncture helps in pain relief by stimulating the pain inhibitory nerve fibers, which lowers the pain input and therefore, relieves the pain. We directly use and raise this effect with electro-acupuncture.
Endorphins: acupuncture stimulates the release of endorphins – the bodys own natural opiates – which result in a reduction of pain and a ‘feel good’ factor. This has been especially closely studied in ear (auricular) acupuncture directed towards those with drug addictions.
Nitric-oxide: acupuncture has been shown to increase the nitric oxide levels in treated regions. This leads to increased local blood circulation and may help in preventing local inflammation and ischemia and relieve the disease condition. We employ these effects when treating local joint pain caused by anything from rheumatism and arthritis to physical injury.
There are many other known physiological effects caused by acupuncture, all giving a partial picture of its effect.