A major study of the effect of acupuncture on osteoarthritis of the knee has found it can both relieve pain and improve movement.
Arthritis patients given acupuncture showed a 40% decrease in pain
The US National Institutes of Health study concludes acupuncture is an effective complement to standard care.
Acupuncture patients showed a 40% decrease in pain, and a nearly 40% improvement in knee function.
Details of the study, which involved 570 patients, are published in Annals of Internal Medicine.
However, the journal editors note that as many people dropped out of the trial, the findings must be treated with some degree of caution.
The patients who took part in the study received either acupuncture, sham acupuncture or guidance on self-help, alongside standard drug treatment.
Sham acupuncture is a procedure designed to prevent patients from being able to detect if needles are actually inserted at treatment points.
Previous studies of acupuncture for osteoarthritis have had conflicting results.
This may have occurred because most studies have included small samples, a limited number of treatment sessions, or other limitations.
Researcher Dr Stephen Strauss, director of the US National Center for Complementary and Alternative Medicine, said: "For the first time, a clinical trial with sufficient rigour, size, and duration has shown that acupuncture reduces the pain and functional impairment of osteoarthritis of the knee.
"These results also indicate that acupuncture can serve as an effective addition to a standard regimen of care and improve quality of life for knee osteoarthritis sufferers."
By eight weeks into the study, the acupuncture patients were showing a significant improvement in knee function, and by 14 weeks their pain levels had dropped sharply compared with the sham acupuncture and self-help groups.
Dr Madeleine Devey, of the Arthritis Research Campaign, said: "It is extremely encouraging to see a well conducted clinical trial on a complementary therapy for OA that demonstrates a positive effect.
"We are also funding a couple of acupuncture trials in the UK and I know that these trials are extremely difficult to undertake.
"Of course these therapies, which appear to alleviate pain and thus improve mobility and function, do not cure or prevent OA, but nevertheless they are a very useful adjunct to other therapies and probably much less damaging than non steroidal anti-inflammatories."
Acupuncture - the practice of inserting thin needles into specific body points to improve health and well-being - originated in China more than 2,000 years ago.
It is based on the idea that energy, or Qi, flows along channels called meridians in body.
Practitioners say the use of needles can block or stimulate these channels.
Some experts believe that the technique may influence the body's electromagnetic fields.
Professor Anthony Woolf, an expert in arthritis at the Royal Cornwall Hospitals Trust, Truro, said previous evidence on the benefits of acupuncture had failed to draw any firm conclusions.
"The finding here suggests acupuncture may be useful as a complementary therapy for people who are already on standard treatments, but not getting full relief," he told the BBC News website.
A separate British study also published in the Annals of Internal Medicine indicated that both genuine and sham acupuncture appeared to help reduce neck pain.
Researchers at the University of Southampton compared genuine and sham treatments from the same therapist on 124 patients with chronic neck pain aged between 18 and 80.
Over 12 weeks, patients from both groups reported a decrease in pain levels of more than 60%.
Dr George Lewith, who co-led the trial, said: "Our study implies that most of the improvement gained from acupuncture was not due to the needling process
itself but due predominantly to the non-specific yet powerful effects which are probably part of the treatment process."