Acupuncture has been part of the medical mainstream in countries such as China and Japan for centuries. It is also one of the most widely utilized forms of alternative therapy in the United States. More than 10 million acupuncture treatments are administered annually in the US alone. In addition, third-party insurance reimbursement and managed care coverage for acupuncture are increasing.

Due to its popularity, scientific investigation of acupuncture has grown dramatically in recent years, with many new studies reported every week. However, the results have been mixed at best.

Simply defined, acupuncture is a treatment method aimed at eliciting a response (such as pain relief) through insertion of very fine needles in the body surface at sites called acupuncture points. A related technique called acupressure (or shiatsu) uses pressure on these points; a related therapy known as electroacupuncture applies electricity to the points.

A wide variety of treatment methods, approaches, techniques, styles, and theoretical frameworks exist within the very broad scope of the term acupuncture. Differences in forms of acupuncture are often cultural; the system of acupuncture practiced in Japan, for example, is quite different from that found in China. Many acupuncturists practice a more or less traditional style called Traditional Chinese Medicine (TCM). Others have adopted modern styles that have little or no reliance on traditional principles.

Acupuncture needles are most often inserted at specific locations on the skin called acupuncture points. These points are located on specific lines outlined by tradition, referred to as meridians or channels. According to Chinese medical theory, there are 14 major meridians that form an invisible network connecting the body surface with the internal organs. Meridians are to conduct Qi, the energy or vital force of the body. Pain or illness is said to result from imbalances or blockages in the flow of Qi through the meridians. Acupuncture is traditionally thought to remove such blockages, restore the normal circulation of Qi, and improve overall health by promoting the balance of energy in the system. However, there is no scientific evidence for the existence of the meridians or Qi itself. (Meridians are not visible under a microscope and, contrary to popular belief, they do not match major nerve pathways.)

In addition to meridians and Qi, the concept of yin and yang is central to acupuncture theory, as it is to all of traditional Chinese philosophy. The terms yin and yang do not represent forces or substances; rather, they are a way to look at the world in terms of the interaction of polar opposites. According to this viewpoint, all movement, growth, and change in the world is a manifestation of the push and pull of these forces. Although seemingly in opposition, these forces are thought to complement and support each other. For example, without rest one cannot exert energy; without becoming tired by exerting energy, it is difficult to sleep. This is just one illustration of the harmony and interaction of yin and yang.

Yang is traditionally associated with heat, power, daylight, summer, and many other active or energetic aspects of life; yin is cold, quiet, and dark. Many illnesses are characterized in terms of an excess or deficiency of either yin or yang, or of both at the same time. For example, when the body is feverish, it is too yang as a whole. There is also a yin and yang balance in each individual organ and part of the body; these can become excessive or deficient, too.

Thus, in TCM, illnesses are described as complex patterns of imbalances and blockages. Treatment is based not on medical diagnosis, but on identifying these problems in the body's energy and seeking to correct them. Does this traditional analysis contain truths about human health or is it just archaic thinking? The answer, as yet, remains unknown.