Acupuncture could be a useful treatment in some cases of chronic pain, according to a study that pooled the results of 29 clinical trials on almost 18,000 people. But the overall benefits were small, compared with no acupuncture or sham acupuncture.

The traditional Chinese treatment involves inserting needles into specific points in the body. Andrew J Vickers of Memorial Sloan-Kettering Cancer Centre in New York led a team of scientists who collated data from previously published, randomised controlled trials on 17,922 patients from the US, UK, Germany, Spain and Swedenwith back and neck pain, osteoarthritis, chronic headache and shoulder pain. "We found acupuncture to be superior to both no-acupuncture control and sham acupuncture for the treatment of chronic pain," wrote Vickers in the September 10 edition of the Archives of Internal Medicine. "Although the data indicate that acupuncture is more than a placebo, the differences between true and sham acupuncture are relatively modest, suggesting that factors in addition to the specific effects of needling are important contributors to therapeutic effects."

The sham treatments used in the studies included needles that had not been fully inserted or devices where the needle retracted into the handle rather than puncturing the skin. Other shams included electrical stimulation.

Vickers found that patients receiving acupuncture had less pain with scores that were 0.23, 0.16 and 0.15 standard deviations lower than sham controls for back and neck pain, osteoarthritis and chronic headaches respectively. In comparison to controls, people who received acupuncture had pain that was 0.55, 0.57 and 0.42 standard deviations lower. The scientists concluded that acupuncture was, therefore, a "reasonable referral option" for patients with chronic pain.

Edzard Ernst, emeritus professor of complementary medicine at the University of Exeter, said the study "impressively and clearly" showed that the effects of acupuncture were mostly due to placebo. "The differences between the results obtained with real and sham acupuncture are small and not clinically relevant. Crucially, they are probably due to residual bias in these studies. Several investigations have shown that the verbal or non-verbal communication between the patient and the therapist is more important than the actual needling. If such factors would be accounted for, the effect of acupuncture on chronic pain might disappear completely."

Ernst added that a potential problem with the trials in the meta-analysis was that, in all cases, the therapist knew whether he or she was administering real or sham acupuncture. "Arguably, it is next to impossible to completely keep this information from the patient. In other words, a trial is either both patient and therapist-blind, or not blind at all. Acupuncturists tend to tell us that therapist blinding is impossible, but this is clearly not true. I fear that, once we manage to eliminate this bias from acupuncture studies, we might find that the effects of acupuncture exclusively are a placebo response."

In an accompanying commentary article in the journal, Andrew Avins of the healthcare consortium Kaiser-Permanente based in Oakland, California, wrote that while it was ideal to understand the mechanism of action of an intervention, the ultimate question was if it worked for the patient.

"At least in the case of acupuncture, Vickers et al have provided some robust evidence that acupuncture seems to provide modest benefits over usual care for patients with diverse sources of chronic pain," wrote Avins. "Perhaps a more productive strategy at this point would be to provide whatever benefits we can for our patients, while we continue to explore more carefully all mechanisms of healing."