The problem with acupuncture is that it makes a large number of claims based on an unsubstantiated premise. The premise is that acupuncture alters the flow of chi (or qi, which seems to be the more favored spelling nowadays) through the body and this is how it effects the body. Although various practioners of various arts claim that they can detect chi through various means, you can’t measure it with any scientific instrument. Thus, we cannot evaluate scientifically whether acupuncture alters the flow of chi, nor what effects the flow of chi has on the body.
There have been few scientific studies on accupuncture. It’s hard to design placebos when the treatment is puncturing the skin with a needle. The studies with the best positive results (such as they are) seem to indicate that acupuncture may provide temporary relief of some pain or nausea. Since acupuncture points tend to be located near clusters of nerve endings, chi flow isn’t necessarily the only explanation. Irritation of the nerves can distract the patient from his/her woes, trigger the release of endorphins, and have other effects on the body. Acupuncture has never been demonstrated to be effective in treating any disease, though it is widely believed that more studies are necessary to determine this conclusively.
I refer you to Cecil , The Skeptics Dictionary, and Quackwatch, and the NIH.