Generally, in the practice of acupuncture, needles varying in length from 1/2 in. (1.27 cm) to several inches are inserted in appropriate points of the body, not necessarily near the affected organ. The needles are twirled and vibrated in specific ways; the depth of insertion also affects the treatment. Modern technique sometimes adds electrical stimulation applied through the needles. The traditional acupuncture points (there are about 800) are arranged along 14 lines, or meridians, running the length of the body from head to foot.

The traditional Chinese explanation of the effectiveness of acupuncture is based on the Taoist philosophy (see Taoism), according to which good health depends on a free circulation of chi (qi), or life-force energy, throughout all the organs of the body. The chi, in turn, depends upon a balance of the two opposing energies of yin (negative, dark, feminine) and yang (positive, bright, masculine). The meridians are the main channels of flow. When energy flow is impeded at any point, e.g., because of a diseased organ or stress, illness in other organs may result. Piercing the channels at the proper points is believed to correct the imbalances.

Western researchers have found that the acupuncture points correspond to points on the skin having less electrical resistance than other skin areas. It has been suggested that acupuncture works by stimulating or repressing the autonomic nervous system in various ways, and there is some evidence that stimulation of the skin can affect internal organs by means of nerve reflex pathways. One theory is that acupuncture stimulates the release of natural pain-relieving chemicals called endorphins. Another is that it stimulates the pituitary gland, which in turn stimulates the adrenal gland to release anti-inflammatory chemicals.

Since the early 1970s, acupuncture has gradually become more accepted in the United States. Many states now accredit schools of acupuncture and administer licensing examinations for nonphysicians. Some physicians are studying and using acupuncture as an adjunct treatment. In the United States acupuncture has been used most often for pain control and drug and alcohol addiction. One impediment to total acceptance is the difficulty of fitting a traditional technique from another culture into the strict methods of scientific clinical trials customary in Western medicine. Studies have shown some benefit from acupuncture, but it is difficult to control for the placebo effect; so-called sham acupuncture, involving the use of needles superficially at points not used in acupuncture, has also shown some pain-relief benefits when used as a control in studies.