Scientists say they have proof that acupuncture works in its own right.
Acupuncture caused brain activity over and above a simple skin prick
Sceptics have said that any benefits gained from acupuncture are merely down to a person's expectation that the treatment will work.
But researchers at University College London and Southampton University say they have separated out this placebo effect.
Their findings, based on a series of experiments and brain scan results, are published in the journal NeuroImage.
The researchers used positron emission tomography (PET) scans to see what was happening in the brains of people having acupuncture treatment for arthritis pain.
Each of the 14 volunteers underwent each of three interventions in a random order.
In one intervention, patients were touched with blunt needles but were aware that the needle would not pierce the skin and that it did not have any therapeutic value.
Another intervention involved treatment with specially developed "trick" needles that give the impression that the skin was being penetrated even though the needles never actually pierced the skin.
The needles worked like stage daggers, with the tip disappearing into the body of the needle when pressure is applied. This was designed to make the patients believed that the treatment was real.
The third intervention was real acupuncture.
When the researchers analysed the patients' PET scan results they found marked differences between the three interventions.
Only the brain areas associated with the sensation of touch were activated when the volunteers were touched with the blunt needles.
During the trick needle treatment, an area of the brain associated with the production of natural opiates - substances that act in a non-specific way to relieve pain - were activated.
This same area was activated with the real acupuncture but, in addition, another region of the brain, the insular, was excited by the treatment.
This was a pathway known to be associated with acupuncture treatment and thought to be involved in pain modulation.
Sarah Williams of the British Acupuncture Council said: "This is very positive news for acupuncture and this latest research is an exciting illustration of what acupuncturists have known for a long time - that acupuncture works and its effectiveness goes beyond the placebo effect."
Professor Henry McQuay, professor of pain relief at the University of Oxford and member of the Bandolier group that looks at the evidence behind different medical treatments, said: "The great bulk of the randomised controlled trials to date do not provide convincing evidence of pain relief over placebo.
"Some people do report that acupuncture makes them feel better.
"But it is extremely difficult, technically, to study acupuncture and tease out the placebo effect."