The benefits of acupuncture are hotly debated
A major review of the effectiveness of acupuncture has concluded that it is hard to find a difference between "true" and "sham" versions.
The research comes just a week after a similar review suggested that both could prevent headache.
It looked at trials involving 3,000 patients with arthritis, migraine, low back pain and post-operative pain.
The results questioned the "traditional foundation" of acupuncture, the British Medical Journal study concluded.
The value of acupuncture remains highly controversial, with conflicting results from many studies.
Much of the argument surrounds the status of "sham" acupuncture, which is frequently used in trials against traditional acupuncture.
While traditional acupuncturists insert needles in acupuncture points located along what they describe as "energy meridians" - a concept for which many scientists say there is no evidence - sham acupuncture places needles away from these points.
However, the needles are still inserted beneath the skin in both varieties, and proponents of non-traditional acupuncture suggest that both varieties may be having a physiological effect - just not in the manner suggested by traditionalists.
The latest review, compiled by the Nordic Cochrane Centre in Copenhagen, found no "clinical relevance" to the differences between traditional and "sham" acupuncture, but found that patients given "sham" acupuncture did experience a small amount pain relief compared to those who had received no treatment.
The authors said that future trials should be trying to work out how much of this effect was due to "placebo" - the effect of undergoing the acupuncture ritual - and how much was a genuine physiological effect.
They said that the findings cast doubt on both traditional acupuncture, and the theory that acupuncture had an important effect on pain.
However, a similar trial carried out by the Cochrane Collaboration last week into the effects of acupuncture in preventing headache and migraine concluded that both sham and traditional acupuncture offered more benefits than conventional painkillers.
Dr Adrian White, a researcher into acupuncture at the Peninsula Medical School in south west England, and a member of the Medical Acupuncture Association, said that "sham" acupuncture might well be having an effect rather than acting as a simple placebo version of the treatment.
"Sham acupuncture often consists of superficial, off point needling, but this may still have a physiological effect.
"Sham controlled studies are of little value in estimating benefits to patients."