At about $50 per session, it's relatively inexpensive and covered by some insurers.

It is also generally safe. About 10% of patients experience some bleeding at the needle sites, although in very rare cases, fatalities have occurred due to infections or injury to vital organs, mostly due to inexperienced practitioners.

Most states require that acupuncturists be licensed, and the Food and Drug Administration requires that needles be new and sterile.

Diagnoses are complicated. An acupuncturist will examine a patient's tongue and take three different pulses on each wrist, as well as asking questions about digestion, sleep and other habits, before determining which meridians may be blocked and where to place the needles. The 14 meridians are thought to be based on the rivers of China, and the 365 points may represent the days of the year. "Invaders" such as wind, cold, heat, dampness, dryness factor into illness, so can five phases known as fire, earth, metal, water and wood.

"It's not like there's a Merck Manual for acupuncture," says Joseph M. Helms, who has trained some 4,000 physicians in acupuncture at his institute in Berkeley, Calif. "Every case is evaluated on an individual basis, based on the presentation of the patient and the knowledge of the acupuncturist."

Dr. Helms notes that Western doctors also examine a patient's tongue for signs of illness. As for qi, he says, while the word doesn't exist in Western medicine, there are similar concepts. "We'll say, 'A 27-year-old female appears moribund; she doesn't respond to stimuli. Or an 85-year old woman is exhibiting a vacant stare.' We're talking about the same energy and vitality, we're just not making it a unique category that we quantify."

Studies in the early 1980s found that acupuncture works in part by stimulating the release of endorphins, the body's natural feel-good chemicals, much like vigorous exercise does.

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