Acupuncture is part of Traditional Chinese Medicine which is thousands of years old. The National Institute of Health, the NIH, has recognized the safety and efficacy of acupuncture for twenty years. There are many different explanations for why acupuncture works such as the needles effecting the flow of qi. The simplest explanation is that acupuncture helps facilitate the body's own healing abilities by increasing blood flow, decreasing inflammation via the insertion of needles into the muscle thus sending a message to the brain to release of endogenous neurotransmitters like opioid peptides.
Website for Jennifer Shulman Acupuncture, a Los Angeles, California acupuncturist.