Chinese medicine theory holds that the human body contains a network of energy pathways through which vital energy, called "chi" (also spelled "qi"), circulates. These pathways are called "meridians."
The meridians contain specific "points" that function somewhat like gates or way stations through which chi flows as it circulates through the body. Acupuncture needles are inserted into these points to regulate the flow of chi through the meridians.
Illness and symptoms are believed to be caused by problems in the circulation of chi through the meridians (e.g., blockage or impairment of proper flow). Good health is considered an indication of the proper circulation of chi - a state of "balance" or "harmony."
Chi is believed to have subtle qualities (sometimes referred to as "elements"), which can be in balance or out of balance, causing symptoms.
Western science has determined that the meridians and points identified in Chinese medicine coincide with anatomical features that can be observed with scientific instruments. For example, electrically-charged particles called "ions" have been found to flow through "ionic streambeds" that correspond with the meridians just beneath the surface of the skin. Acupuncture points have been found to emit light, which can be detected with sensitive laboratory equipment.
The chi proposed by Chinese medicine theory is not electricity and is not directly detectable with scientific instruments. Western science has studied electrical phenomena (ions, electrons, electrical energy) that occur with acupuncture. These phenomena are detectable and appear to accompany the circulation of chi through the body.
Acupuncture has been shown to effectively treat some health conditions, including pain. However, the mechanism of action remains unclear. Endogenous opioid-mediated mechanisms of electroacupuncture as used in China only appear to explain how acupuncture works in part. Acupuncture is purported to also affect the brain's reward systems as well as blood flow in the skin, muscles, and nerves. Research has also shown regional effects on neurotransmitter expression.
One of the challenges in reviewing acupuncture and other complementary practices is the lack of placebo or sham-groups in most clinical trials. Some experts argue that blinding and placebo controls are not necessary, since when they are used, they are often not true shams. Recent study investigated a sham retractable type acupuncture needle and found that the applicability of "placebo" needling may be influenced by inter-tester variability, as well as the patient's knowledge and experience of acupuncture, acupuncture point selection, the visual impact of needling, and so on.