According to the National Institutes of Health:

Preclinical studies have documented acupuncture 's effects, but they have not been able to fully explain how acupuncture works within the framework of the Western system of medicine that is commonly practiced in the United States.

In 1997, the National Institutes of Health (NIH) issued a consensus statement on acupuncture that concluded that

there is sufficient evidence of acupuncture 's value to expand its use into conventional medicine and to encourage further studies of its physiology and clinical value

The NIH consensus statement said that:

the data in support of acupuncture are as strong as those for many accepted Western medical therapies

and added that

there is clear evidence that needle acupuncture is efficacious for adult postoperative and chemotherapy nausea and vomiting and probably for the nausea of pregnancy... There is reasonable evidence of efficacy for postoperative dental pain... reasonable studies (although sometimes only single studies) showing relief of pain with acupuncture on diverse pain conditions such as menstrual cramps, tennis elbow, and fibromyalgia...

The NIH consensus statement summarized and made a prediction:

Acupuncture as a therapeutic intervention is widely practiced in the United States. While there have been many studies of its potential usefulness, many of these studies provide equivocal results because of design, sample size, and other factors. The issue is further complicated by inherent difficulties in the use of appropriate controls, such as placebos and sham acupuncture groups. However, promising results have emerged, for example, showing efficacy of acupuncture in adult postoperative and chemotherapy nausea and vomiting and in postoperative dental pain. There are other situations such as addiction, stroke rehabilitation, headache, menstrual cramps, tennis elbow, fibromyalgia, myofascial pain, osteoarthritis, low back pain, carpal tunnel syndrome, and asthma, in which acupuncture may be useful as an adjunct treatment or an acceptable alternative or be included in a comprehensive management program. Further research is likely to uncover additional areas where acupuncture interventions will be useful.

Commenting on the relative safety of acupuncture compared to other treatments, the NIH consensus panel stated that "(a)dverse side effects of acupuncture are extremely low and often lower than conventional treatments." They also stated:

"the incidence of adverse effects is substantially lower than that of many drugs or other accepted medical procedures used for the same condition. For example, musculoskeletal conditions, such as fibromyalgia , myofascial pain , and tennis elbow ... are conditions for which acupuncture may be beneficial. These painful conditions are often treated with, among other things, anti-inflammatory medications (aspirin, ibuprofen, etc.) or with steroid injections. Both medical interventions have a potential for deleterious side effects but are still widely used and are considered acceptable treatments."

In a Japanese survey of 55,291 acupuncture treatments given over five years by 73 acupuncturists, 99.8% of them were performed with no significant minor adverse effects and zero major adverse incidents (Hitoshi Yamashita, Bac, Hiroshi Tsukayama, BA, Yasuo Tanno, MD, PhD. Kazushi Nishijo, PhD, JAMA). Two combined studies in the UK of 66,229 acupuncture treatments yielded only 134 minor adverse events. (British Medical Journal 2001 Sep 1). The total of 121,520 treatments with acupuncture therapy were given with no major adverse incidents (for comparison, a single such event would have indicated a 0.002% incidence).